Imaging element having a photoluminescent tag and process of using the imaging element to form a recording element

ABSTRACT

The invention relates to an imaging element and a method of using the imaging element to form a recording element. The imaging element includes a composition sensitive to actinic radiation from a source of radiation having a range of wavelengths and a photoluminescent tag that is responsive to at least one wavelength from the source of radiation. The photoluminescent tag can be used to authenticate the identity of the element, provide information about the element, and/or to establish one or more conditions in a device used to prepare the recording element from the imaging element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to an imaging element for use as a recordingelement and a process for preparing the recording element from theimaging element. In particular, this invention relates to aphotosensitive imaging element having a photoluminescent tag disposedtherein. More particularly, this invention relates to a photosensitiveimaging element for use as a printing form, and a process for preparingthe form from the element.

2. Description of Related Art

Polymer products are used as components of imaging and photosensitivesystems and particularly in photoimaging systems such as those describedin “Light-Sensitive Systems: Chemistry and Application of NonsilverHalide Photographic Processes” by J. Kosar, John Wiley & Sons, Inc.,1965 and more recently in “Imaging Processes And Material—Neblette'sEight Edition” edited by J. Sturge, V. Walworth and A. Shepp, VanNostrand Reinhold, 1989. In such systems, actinic radiation impinges ona material containing a photoactive component to induce a physical orchemical change in that material. An image or latent image is formedwhich can be thereby be processed into a useful image forming arecording element. Typically actinic radiation useful for imaging islight ranging from the near ultraviolet through the visible spectralregions, but in some instances may also include infrared,deep-ultraviolet, X-ray, and electron beam radiation.

Although the polymer product itself may be photoactive, generally aphotosensitive composition contains one or more photoactive componentsin addition to the polymer product. Upon exposure to actinic radiation,the photoactive component acts to change the rheological state, thesolubility, the surface characteristics, refractive index, the color,the electromagnetic characteristics or other such physical or chemicalcharacteristics of the photosensitive composition as described in theNeblette's publication supra.

Polymer products are particularly useful in photopolymerizable systemssuch as disclosed in Chapter 7 of the Neblette's publication supra. Suchphotopolymerizable systems typically have at least one additionpolymerizable monomeric component having one or more sites of terminalethylenic unsaturation, and one or more polymers as a binding agent.Frequently the binding agent is a polymer, or simple polymer blend,i.e., an intimate mixture of two or more polymers. During imagingexposure, the monomeric component polymerizes and/or crosslinks to forma polymer or polymer network in which at least some of the polymericbinding agent is entrapped thereby rendering a change in the physical orchemical characteristics, that is, typically photohardening orinsolubilizing, the exposed area or areas.

Some examples of imaging systems include photopolymer and resist systemsfor use as printing plates, pre-press proofs, and resists in circuitboard and chips; and press printing systems, such as lithography,gravure, letterpress, flexography, and screens, for use in pressprinting and circuit board printing. For each end-use application of thepolymer products a plethora of imaging elements exist due to the numberof manufacturers as well as the variety of products provided by each ofthe manufacturers to address particular needs in end-use situations. Anyone end-user facility may have a number of imaging products available tomeet their and their customer's needs, but it may be difficult tomonitor consumption and appropriate process conditions to convert theimaging product into desired recording material. From an end user'sstandpoint, it is desirable to be able to identify the imaging elementshould it become separated from its packaging. From the manufacturer'sstandpoint, when assisting the end-users and/or accepting a returnedimaging product it is desirable to verify that the imaging product is infact one made by the manufacturer, not from another manufacturer, andnot a counterfeit product. Thus it is desirable for users to be able toauthenticate the identity of the imaging element.

Furthermore, each imaging element typically undergoes a process ofmultiple steps on one or more different devices that are used to convertthe imaging elements into useful recording product. Devices usedinclude, for example, actinic radiation exposure units, laser-radiationexposure units and imagers, processors for removing selected compositionmaterial with heat or with a solution, processors for developing latentimage with heat or with a solution, and lamination units for formingassemblages with the imaging element or other supports. The setup foreach device can be complex and dependent upon the particular variety ofimaging element being worked on. Each step in the process of formingrecording elements for imaging element involves multiple parameters thatneed to be set appropriately to extract the optimum performance of theimaging element and create the desired recording element that satisfiesthe end user's needs. Thus, it is desirable to not only identify theimaging element, but also to use this identification information todirect the establishment of the parameters in the variety of devicesused in the imaging process automatically without the need for humanintervention.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided an imaging elementcomprising a composition sensitive to actinic radiation from a source ofradiation having a range of wavelengths, wherein a photoluminescent tagis disposed in the element and is responsive to at least one wavelengthfrom the source of radiation.

In accordance with another aspect of this invention there is provided amethod for making a recording element from the imaging element thatcomprises exposing the imaging element to the actinic radiation to formthe recording element.

In accordance with another aspect of this invention there is provided amethod for setting conditions in a device used for making a recordingelement. The method includes exposing the imaging element to the atleast one wavelength to generate an emitted radiation from the tag at awavelength that is different from the actinic radiation, detecting theemitted radiation, and setting one or more conditions for the operationof the device according to the detected emission.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention concerns an imaging element and a process of usingthe imaging element to form a recording element. The imaging elementcomprises a composition sensitive to actinic radiation from a source ofradiation having a range of wavelengths. The imaging element includes aphotoluminescent tag that is responsive to at lease one wavelength fromthe source of radiation. The imaging element includes thephotoluminescent tag that can be used to authenticate the identity ofthe element, to provide information about the element, and/or toestablish one or more conditions in a device used to prepare a recordingelement from the imaging element. The process of authenticating theidentity of or providing information about the imaging element havingthe photoluminescent tag responsive to at least one wavelength from asource of actinic radiation is simplified by using the same source ofactinic radiation for the imaging element and to elicit a response ofthe tag. This avoids the need to use a separate source of radiation toelicit a response from the tag. The photoluminescent tag may also bereferred to herein as tag, tag material, tag compound, photoluminescentmaterial, or photoluminescent compound.

Various embodiments of the imaging element of the present invention areintended for use as recording elements, including, but are not limitedto, printing forms, pre-press proofs, resists, and color filters.Resists are used in the formation of circuit patterns in circuit boardsand chips. Printing forms include recording elements used forflexographic, letterpress, gravure, and lithographic printing. Theimaging element for printing end-use can be of any shape or formincluding plates and cylinders.

It is surprising that the sensitometric properties of the imagingelement do not change or deteriorate as a result of the presence of thephotoluminescent tag material in the element. The presence of anadditive, such as the photoluminescent tag, as a particulate or otherabsorbing material in the element tends to reduce the penetration of theactinic radiation required to alter the physical or chemicalcharacteristics of the composition layer. If the composition layer isinsufficiently altered by exposure to actinic radiation, the imagingelement will not successfully achieve the required end-use propertiesfor the recording element. Particularly when the tag compound is aninorganic particulate form, it is quite surprising that their presencedoes not cause scatter of the actinic radiation used to image thephotosensitive composition.

Unless otherwise indicated, the following terms as used herein have themeaning as defined below.

“Actinic radiation” refers to radiation capable of initiating reactionor reactions to change the physical or chemical characteristics of aphotosensitive composition.

“Chelate” and its variants, refers to the type of coordination compoundin which a central metal ion is attached by coordinate links to two ormore nonmetal atoms in the same molecule, called ligands. Heterocyclicrings are formed with the central (metal) atom as part of each ring.

“Coordination compound”, which may also be referred to as a “complexcompound”, refers to a compound formed by the union of a metal ion witha nonmetallic ion or molecule called a ligand or complexing agent.

“Complex”, when used as a noun, refers to a compound having at least onemetallic ion and at least one ligand.

“Excitation” refers to a process in which an atom or molecule gainsenergy from electromagnetic radiation or from collision raising it to anexcited state.

“Excitation energy” refers to the energy required to change a systemfrom its ground state to a particular excited state.

“Fluorescence” and “Fluorescent” refers to a phenomenon in which amaterial releases or emits energy immediately following excitation, oremission following with a delay shorter than 10⁻⁸ seconds.

“Group” refers to a part of a compound, such as a substituent in anorganic compound or a ligand in a complex.

“Ligand” refers to a molecule, ion, or atom that is attached to thecentral atom of a coordination compound, a chelate, or other complex,usually a metal ion or atom. Ligands offering two groups for attachmentto the metal are termed bidentate; three groups, tridentate, etc.

“Luminescence” and “Luminescent” refers to a phenomenon in which asubstance is excited by an external energy source and emits this energyin the form of light and/or radiation.

“Phosphor” refers to a substance either, organic or inorganic, liquid orcrystalline, that is capable of luminescence.

“Phosphorescence” and “Phosphorescent” refers to materials that havestored energy by excitation, and that release the stored energygradually over an period of time without the need for externalstimulation.

“Photoluminescent” and “Photoluminescence” refers to luminescencestimulated or excited by visible, infrared, or ultraviolet radiation.

“Stimulated emission” refers to the phenomena in which a substance thathas stored energy by excitation, and releases the stored energy onlyafter being excited with an external stimulating energy source.

“Visible radiation or light” refers to wavelengths of radiation betweenabout 390 and 770 nm.

“Infrared radiation or light” refers to wavelengths of radiation betweenabout 770 and 10⁶ nm.

“Ultraviolet radiation or light” refers to wavelengths of radiationbetween about 10 and 390 nm.

Note that the provided ranges of wavelengths for infrared, visible, andultraviolet are general guides and that there may be some overlap ofradiation wavelengths between what is generally considered ultravioletradiation and visible radiation, and between what is generallyconsidered visible radiation and infrared radiation.

The imaging element comprises a composition sensitive to actinicradiation, that is, the imaging element includes a layer of thecomposition that is photosensitive. The term “photosensitive” encompassany system in which the photosensitive composition is capable ofinitiating a reaction or reactions, particularly photochemicalreactions, upon response to actinic radiation. Upon exposure to actinicradiation, chain propagated polymerization of a monomer and/or oligomeris induced by either a condensation mechanism or by free radicaladdition polymerization. While all photopolymerizable mechanisms arecontemplated, the compositions and processes of this invention will bedescribed in the context of free-radical initiated additionpolymerization of monomers and/or oligomers having one or more terminalethylenically unsaturated groups. In this context, the photoinitiatorsystem when exposed to actinic radiation can act as a source of freeradicals needed to initiate polymerization of the monomer and/oroligomer. The monomer may have non-terminal ethylenically unsaturatedgroups, and/or the composition may contain one or more other components,such as a monomer, that promote crosslinking. As such, the term“photopolymerizable” is intended to encompass systems that arephotopolymerizable, photocrosslinkable, or both. As used herein,photopolymerization may also be referred to as curing.

The photoluminescent tag is responsive to radiation used to convert theimaging element into a recording element. The photoluminescent tag canbe responsive to visible, infrared, or ultraviolet radiation, as can theimaging element. The response of the photoluminescent tag to thestimulation, excites the tag to an energized state, and emits energy asradiation, preferably as light. The tag may emit energy immediately orsubstantially immediately (i.e., delay shorter than 10⁻⁸ seconds)whereby the tag exhibits fluorescence. Alternatively the excited tag maystore the energy and release the stored energy gradually over a periodof time without the need for external stimulation, whereby the tagexhibits phosphorescence. In fluorescence and phosphorescence phenomena,typically the emitted radiation is of a longer wavelength of radiationthan that used to excite the tag. In another alternative, the excitedtag may store the energy and release the stored energy only after beingstimulated externally with a different wavelength, whereby the tagexhibits stimulated emission. The tag that exhibits stimulated emissionmay be excited to store the energy by the photoreaction exposure or whenthe tag compound is produced. Excitation of the photoluminescent tag isstimulation to elicit a response that encompasses fluorescence,phosphorescence, and/or stimulated emission. It is also possible thatthe photoluminescent tag exhibits more than one type of emission, thatis, exhibits fluorescence and phosphorescence; or phosphorescence andstimulated emission; or fluorescence and stimulated emission; orfluorescence, phosphorescence, and stimulated emission. Typically theemitted radiation is at a wavelength different from the wavelength ofradiation used for stimulating the tag.

The photoluminescent tag is disposed in the imaging element. As will bedescribed below, the imaging element has a composition sensitive toactinic radiation, which in one embodiment is a photosensitivecomposition, forming a layer of the element. The imaging element canalso include one or more additional layers. The photoluminescent tag maybe disposed in any one or more of the layers, i.e., photosensitiveand/or additional layers, associated with the imaging element, byincorporation into a composition forming any one or more layers of theelement. The composition forming one or more additional layers may alsobe reactive to actinic radiation, which can be different from theactinic radiation used for the photosensitive layer. It is alsocontemplated that the imaging element can contain more than onephotoluminescent tag compounds. In one embodiment the photoluminescenttag is included in the composition that is sensitive to actinicradiation. In an alternate embodiment, the photoluminescent tag isincluded in one or more additional layers that are not sensitive to theactinic radiation. In yet another embodiment, the photoluminescent tagis included in a second composition layer that is sensitive to actinicradiation, but the second composition layer is different from thecomposition layer forming the primary photoreaction layer (i.e.,photopolymerizable layer). The additional layer may be directly adjacentor non-adjacent the composition layer sensitive to actinic radiation.The additional layer may be integral with the imaging element or may beassociated in a separate element that can form an assemblage with theimaging element. The additional layer may have one or more functions forthe imaging element in addition to the function/s associated with thepresence of the photoluminescent tag in the element. Alternatively, theimaging element may include the photoluminescent tag in its own layerindependent of one or more of the additional functional layers. Inembodiments where the photoluminescent tag material is included in theadditional layer, the additional layer is present during the exposure ofthe imaging element to actinic radiation. In the case where the tag isincorporated into its own layer, the tag layer need not fully cover theother functional layer/s of the element, and can form a “detectingstrip” for the imaging element, for example, along a side or middle ofthe element. The detecting strip may overlap with the image region ofthe imaging element or recording element.

The photoluminescent tag may be present in the imaging element for allor only a portion of the process steps necessary to convert the imagingelement into a recording element. For example, the tag may be includedin the photosensitive layer of an imaging element for use as a printingform. The tag would be present in the imaging element for the steps ofexposing to actinic radiation and treating to create the structure forprinting, and thereby be present in the final printing form. Alternatelythe tag may be included in a temporary layer for the imaging elementwherein the tag is only present in the imaging element for one (or more)of the steps forming the recording element, and thereby not be presentin the recording element. For example, the tag may be incorporated intoa temporary layer in the imaging element for use as a printing form,such that the tag is present during exposure to actinic radiation step,but is removed during a treating step that creates the printing form.

The imaging element includes a composition sensitive to actinicradiation and capable of being exposed with a source of radiation havinga range of wavelengths that encompasses the actinic radiation. Thephotoluminescent tag is disposed in the imaging element and isresponsive to one or more wavelengths of radiation in the range ofwavelengths from the source of radiation. The composition is responsiveto actinic radiation at a first wavelength (or range of wavelengths) andthe photoluminescent tag is responsive to radiation at a secondwavelength (or range of wavelengths). (Hereinafter unless otherwiseindicated, a wavelength can be a single wavelength or a range ofwavelengths (i.e., spectra) encompassing the particular wavelength.) Inone embodiment, the second wavelength can be the same as orsubstantially the same as, the first wavelength. That is, the tag has anabsorption spectrum for its response to be excited or stimulated thatcan overlap, in whole or in part, with an absorption spectrum of theimaging element induced by the actinic radiation. In another embodiment,the second wavelength can be different from, or substantially differentfrom, the first wavelength, however, both the first wavelength and thesecond wavelength are encompassed by the range of wavelengths emitted bythe source of radiation used to expose the imaging element and inducereaction of the composition. In yet another embodiment, the secondwavelength can be different from, or substantially different from, thefirst wavelength, however, both the first wavelength and the secondwavelength are encompassed by the range of wavelengths emitted by asource of radiation used in one or more of the process steps to convertthe imaging element into a recording element.

It is advantageous that the photoluminescent tag is responsive to thesame or substantially the same (range of) wavelength used for at leastone of the imaging steps that convert the imaging element to therecording element since the process of preparing a recording elementfrom the imaging element is simplified and requires no separateillumination steps to elicit the response from the tag. Anotheradvantage is that the need for a second source of radiation toilluminate the imaging element (or recording element) and elicit theresponse from the tag is eliminated. It is particularly advantageousembodiment in which the photoluminescent tag is responsive to the sameor substantially the same (range of) wavelength from the source ofactinic radiation as the photoreactive system in the imaging element.The photosensitive composition in most conventional imaging elements issensitive to ultraviolet radiation (i.e., the actinic radiation). Byincluding in the imaging element a photoluminescent tag that is alsoresponsive to at least one wavelength of the ultraviolet radiation (usedfor the photosensitive composition), the tag can be excited orstimulated at the same time and by the same source that the imagingelement is exposed to the actinic ultraviolet radiation.

The response of the photoluminescent tag to radiation that excites orstimulates the tag is to emit radiation at a wavelength or range ofwavelengths suitable for observation or detection by sensors. Theradiation emitted by the tag should not overlap or substantially overlapinto the wavelength (or range of wavelengths) that is capable ofinitiating reaction or reactions to change the physical or chemicalcharacteristics of the imaging element. In a particular embodiment, theradiation emitted by the tag should not overlap or substantially overlapinto the wavelength (or range of wavelengths) at which actinic radiationinitiates the photoreactive response of the photosensitive composition.The radiation emitted by the tag may overlap slightly with the actinicradiation wavelength, provided that the emission of the tag does notinfluence or detrimentally impact the conversion of the imaging elementto a recording element, or the use of the recording element. In oneembodiment, the response of the photoluminescent tag to exposure toultraviolet radiation is excitation or stimulation to emit radiation ata wavelength or range of wavelengths in visible light, such that thehuman eye can observe the response of the tag. A sensor can also be usedto detect the response of the tag. In another embodiment, the responseof the photoluminescent tag to exposure to excitation or stimulationradiation is to emit radiation at a wavelength or range of wavelengthssuch that only a sensor can detect the presence of the tag in theimaging element. One advantage of using a tag that emits visibleradiation is that the sensors used to detect the visible radiation arerelatively inexpensive and readily available.

In one embodiment, the imaging element has a photopolymerizablecomposition that is sensitive to ultraviolet radiation between about 350to 380 nm and includes the photoluminescent tag that is responsive toultraviolet radiation between about 360 to 380 nm. In anotherembodiment, the imaging element has a photopolymerizable compositionthat is sensitive to ultraviolet radiation between about 340 to 380 nmand includes the photoluminescent tag that is responsive to ultravioletradiation between about 320 to 345 nm. In each of these embodiments, thetag would respond upon exposure to a source of radiation that providesultraviolet light between about 320 to 380 nm. An embodiment of theimaging element is also contemplated in which the photopolymerizablecomposition includes the photoluminescent tag that is responsive toultraviolet radiation between about 240 to 260 nm. In this embodimentthe tag would respond to ultraviolet exposure from a source emittingbetween about 200 and 300 nm, and, if the imaging element (or recordingelement) is for use in flexographic printing, the exposure to actinicradiation from the source to detackify the printing surface of theelement. In one embodiment, the composition of the imaging element issensitive to infrared radiation, and the tag is also responsive toinfrared radiation. In yet another embodiment, the imaging elementincludes the photoluminescent tag that is responsive to infraredradiation, and a layer of a composition sensitive to infrared radiationthat upon exposure to actinic infrared radiation may transfer or causeanother adjacent layer to transfer to a substrate. Another embodiment ofthe imaging element is also contemplated in which the photoluminescenttag responsive to infrared radiation is incorporated into a compositionlayer other than the photopolymerizable layer, such as a mask-forminglayer of the imaging element. The tag would respond to exposure of theinfrared radiation that ablates the mask-forming layer to create themask on the imaging element. It is encompassed within this inventionthat exposure of a layer of a composition sensitive to actinic radiationmay be capable of changing the physical characteristic/s of the layer,e.g., adhesion balance, ablation, etc.

The photoluminescent tag can be included in the composition sensitive toactinic radiation or in any other additional layer, or in its own layerfor the imaging element. The photoluminescent tag can be incorporatedwith a component that allows for dispersing of the tag in thecomposition and uniform distribution of the tag in a layer suitable foruse with the imaging element. The layer containing the tag can beprepared by conventional methods by combining the tag with the one ormore components. In one embodiment, the tag that is in particulate formmay suitably disperse within one or more of the liquid or liquid-likecomponents in the composition. It is advantageous to use the particulatetag that can easily disperse in various components in the composition asit simplifies the preparation of the composition and the imagingelement. In other embodiments, the tag that is in particulate form mayhave difficulty dispersing in a liquid-like component. In suchembodiments, a dispersant can be added in order to disperse the tagparticles and avoid flocculation and agglomeration. A wide range ofdispersants are commercially available. Suitable dispersants are the A-Bdispersants generally described in “Use of A-B Block Polymers asDispersants For Non-aqueous Coating Systems” by H. K. Jakubauskas,Journal of Coating Technology, Vol. 58; Number 736; pages 71-82. UsefulA-B dispersants are disclosed in U.S. Pat. Nos. 3,684,771; 3,788,996;4,070,388; and 4,032,698. The dispersant is generally present in anamount of about 0.1 to 10% by weight, based on the total weight of thelayer. In another embodiment when the tag is a particulate, the tag isincorporated with a binder. When the tag is incorporated into its ownlayer, the tag can be combined with a polymeric binder which can beselected from the binders described as suitable for use in thephotosensitive layer and the additional layers, and which can be thesame or different from the binder used in the photosensitive layerand/or the additional layers. One method for preparing the compositioncontaining the tag is to precompound the tag with a portion of the totalamount of binder, and then add the remaining portion of the binder tothe precompounded mixture. Adding of the precompounding mixture to theremaining portion of the binder encompasses diluting, mixing, and/orblending. At any point in the precompounding, a solvent can be used fordispersing the materials used in the diluting, mixing, and/or blendingsteps. The weight ratio of the precompounded mixture to the remainingbinder portion is preferably 1:10000 to 1:100. This is done to ensurethat the particulate tag material is well dispersed in the binder anduniformly distributed in the layer. In this way, the photoluminescenttag will respond to exposure similarly when detected in an imaged areaor in a non-imaged area of the imaging element. The weight ratio ensuresthe level at which the tag is included in the imaging element. The lowerthe concentration of the tag the more difficult it is to detect itspresence; however, the lower the concentration of the tag the lessimpact the tag may have on the imaging process.

The tag is present in the imaging element in an amount sufficient toelicit a response when exposed to radiation from at least one wavelengthfrom the source of radiation. When the photoluminescent tag is presentin the composition sensitive to actinic radiation, the tag can be inconcentrations from 1 to 1000 parts per million (ppm) (1 ppm to 0.1weight %) based on the total components in the layer, preferably lessthan 750 ppm, more preferably less than 500 ppm, and most preferablyless than 200 ppm. When the photoluminescent tag is present in one ormore of the additional layers, it may be possible and sometimesnecessary for the tag to be present in concentrations less than 100 ppm,preferably less than 50 ppm, based on total components in the layer.When the tag is disposed in or on the support of the photosensitiveelement, it may be sufficient for the tag to be present in 1 to 20 ppm.In any case, the tag may be present in the photosensitive composition,or in one or more of the additional layers, or in the support in greaterthan the suggested amounts. The amount of tag needed to provide desiredfunctionality in the imaging element, can depend on the thickness of thelayer that the tag is incorporated, the concentration of actinicradiation absorbers, e.g., photoinitiators, the solubility ordispersibility of the tag in the layer, and the efficacy of the tag.

The photoluminescent tag that is an inorganic typically is inparticulate form. A suitable size of particles is less than the smallestwavelength of light used to create the recording element. This is wouldmitigate any light scattering during the exposure/s due to the presenceof the particles. For example, in the case of an UV-imaged printingplate, as the dominant wavelength used to create the three-dimensionalimage is 365 nm, the suitable size for the particles is expected to beless than 0.365 microns. However, surprisingly, it was found that aslong as the concentration of the particles is below 1000 ppm, the sizeof tag particles can be as high as 10 microns. Thus a suitable range oftag particle size is about 0.2 microns to 10 microns. Smaller particlesizes, that is, particles less than 0.2 microns to as small asnanoparticles (100 nm or less) could also be used, provided thatagglomeration of the particulate can be avoided. Nanometer sizeparticles can be produced by aerosol decomposition, spray pyrolysis,combustion, hydrothermal, or sol gel type processes. It should be notedthat to a certain extent, the size of the particles may be impacted bythe feature size that needs to recorded on the element. The smaller thefeature size of the recording image the smaller the size scale of theparticles. Examples of this trade-off can be encountered inphotoresists.

The photoluminescent tag is not limited and can include inorganicphotoluminescent materials and organic photoluminescent materials.Photoluminescent tag encompasses materials that exhibit fluorescence,phosphorescence, and/or stimulated emission. Organic photoluminescentmaterials can be incorporated into the composition provided that the tagis compatible with the constituents in the composition. By compatibilityis meant the ability of two or more constituents to remain dispersedwith one another without causing appreciable scattering of actinicradiation. Compatibility is often limited by the relative proportions ofthe constituents and incompatibility is evidenced by formation of hazein the composition. Some light haze of layers formed from suchcompositions before or during exposure can be tolerated, but preferablyhaze is avoided. The amount of tag used is therefore limited to thosecompatible concentrations below that which produces undesired lightscatter or haze.

Suitable photoluminescent tag materials can include, but are not limitedto, inorganic compounds, small molecule organic fluorescent compounds,conjugated polymers, photoluminescent metal complexes that can includefluorescent and phosphorescent metal complexes, and mixtures thereof.Examples of small molecule organic fluorescent compounds include, butare not limited to, pyrene, perylene, coumarin, rubrene, derivativesthereof, and mixtures thereof. Examples of conjugated polymers include,but are not limited to poly(phenylenevinylenes), polyfluorenes,poly(spirobifluorenes), polythiophenes, poly(p-phenylenes), copolymersthereof, and mixtures thereof.

In the case of organic photoluminescent materials, the tag does notencompass compounds that are considered optical brighteners. Opticalbrighteners, also known as optical bleach, colorless dye, fluorescentbrightener, is a colorless fluorescent organic compound which absorbsultraviolet light and emits it as visible blue light, but is present atsuch low concentration that it overall whitens the color, but does notturn blue.

Suitable inorganic photoluminescent tag materials are disclosed by Kabayet al. in U.S. Pat. No. 4,857,228. which is hereby incorporated byreference in its entirety. The photoluminescent tags can be acrystalline matrix including sulfur (sulphur), selenium, and an alkalineearth metal selected from the group consisting of calcium, strontium,and combinations thereof. The tag also includes one or more activatorsdispersed in the matrix. The activators and the matrix cooperativelydefine active sites for emission of electromagnetic radiation. Theactivators are preferably heavy metals or transition metals, such aseuropium (Eu), samarium (Sm), and bismuth (Bi). Combinations ofactivators can also be used.

Other suitable inorganic photoluminescent tag materials are disclosed bySugita et al. in GB 2063904 A which is hereby incorporated by referencein its entirety. The inorganic photoluminescent tags are phosphors ofcarbonates, sulphates, silicates, sulfides, oxides, or halides of onethe following: calcium, beryllium, magnesium, strontium, barium,lithium, sodium, zinc, aluminum, lead. The phosphor is combined with anactivator selected from the group consisting of strontium, magnesium,tin, bismuth, boron, manganese, lead, chromium, copper, lanthanum,neodymium, europium, samarium, thulium, yttrium, terbium.

Still further suitable examples of photoluminescent tag compounds aredisclosed by Soled et al. in EP 0339 895 A1 which is hereby incorporatedby reference in its entirety. The photoluminescent tag compoundscomprise an alkaline earth chalcogenide host and europium and thuliumactivators. The host is represented by the formula comprising M:Xwherein M is selected from the group consisting of magnesium, calcium,strontium, barium, and mixtures thereof, and X is selected from thegroup consisting of sulfur, selenium, and mixtures thereof. The europiumand thulium activator can be oxides, sulfates, carbonates, nitrates,halides or mixtures thereof.

Photoluminescent tag compounds can include Anti-Stokes phosphors.Anti-Stokes phosphors refers to compounds in which the energy emitted isgreater than the energy absorbed, that is, the wavelength of radiationemitted from the phosphor is shorter than the wavelength of theradiation that is used to stimulate or excite the phosphor. Thesephosphors are capable of converting comparatively low-energy infraredexcitation radiation into high-energy radiation wherein the radiationemitted can be in the visible as well as in the invisible range. Suchphosphors include thulium-activated and ytterbium co-doped oxysulfidesas disclosed by Paeschke et al. in U.S. Publication 2002/0130304 whichis hereby incorporated by reference in its entirety. The oxysulfide maybe based upon a matrix using gadolinium, yttrium, lanthnum, andlutetium. Also suitable are the oxysulfide anti-Stokes phosphorsdisclosed by Bratchley et al. in GB 2,258,659 and GB 2,258,660 which arehereby incorporated by reference. The oxysulfide phosphor uses Y₂O₂S asthe basic lattice material. Also suitable are the oxysulfide anti-Stokesphosphors disclosed by Muller et al. in WO00/60527 which is herebyincorporated by reference, wherein the phosphors are Y₂O₂S:Yb, Er,Y₂O₂S:Yb, Tm and Gd₂O₂S:Yb, Er. Particularly preferred photoluminescenttag compounds are metal oxysulfides that are infrared excited phosphors.

Other suitable photoluminescent tag materials are photoluminescent metalcomplexes. Metal complexes are compounds formed by the union of a metalion with a nonmetallic ion or molecule called a ligand or complexingagent. The metal complex may be chelated, or non-chelated, or maycontain both chelated and non-chelated coordination links to the metalion. Suitable metals that form metal complexes include rare earthmetals, transition metals of columns 3 through 13 of the Periodic Table.The metals can be heptacoordinate or octacoordinate. Rare earth metalsinclude metals in the lanthanide series and in the actinide serieshaving an oxidation state of +2 or +3. Examples of suitable metals inthe lanthanide series include, but are not limited to, europium (Eu),terbium (Tb), and thulium (Tm). Examples of suitable transition metalsinclude, but are not limited to, iridium (Ir), rhodium (Rh), osmium(Os), platinum (Pt), and ruthenium (Ru).

The metal of the photoluminescent metal complex includes one or more ofcoordination sites that are occupied by at least one ligand. More thanone ligand, and more than one type of ligand may be coordinated to themetal. Suitable ligands include halides; β-enolates (which may also becalled β-diketones); anions of acids, such as acetic acid, benzoic acid,picolinic acid, and dipicolinic acid; diimines; phosphines and phsphineoxides; and nitrogen-containing ligands, such as amines, polyamines,pyridines, arylamines, bipyridine, terpyridine, phenanthrolines, andtetramethylenediamine. Other suitable ligands include quinolates; andcarboxylates. Additional examples of suitable ligands are tripyridyl and2,2,6,6-tetramethyl-3,5-heptanedionate (TMHD); a, a′, a″ tripyridyl;crown ethers; phthalocyanines; porphyrines; ethylene diamine tetramine(EDTA); 1,2diaminocyclohexanetetraacetic acid (DCTA);diethylentriaminepentaacetate (DTPA), triethyleneaminehexaacetic acid(TTNA); and diphenylphosphonimide triphenyl phosphorane (OPNP).

Examples of photoluminescent metal complexes include, but are notlimited to, metal chelated oxinoid compounds, such astris(8-hydroxyquinolato)aluminum (Alq₃); Schiff base complexes of Al andZn; cyclometalated iridium and platinum photoluminescent compounds, suchas complexes of Iridium with phenylpyridine, phenylquinoline, orphenylpyrimidine ligands as disclosed in Petrov et al., Published PCTApplication WO 02/02714, and organometallic complexes described in, forexample, published applications US 2001/0019782, EP 1191612, WO02/15645, and EP 1191614; and mixtures thereof.

Metal quinolates may be used such as lithium quinolate, and metalcomplexes of non-rare earth metals such as aluminum, magnesium, zinc,and scandium complexes. Examples of non-rare earth metal complexes withβ-diketones e.g., tris-(1,3-diphenyl-1-3-propanedione) (DBM) as theligand, include Al(DBM)₃, Zn(DBM)₂, Mg(DBM)₂, Sc(DBM)₃, etc.

In one embodiment, the photoluminescent tag is a metal complex of arare-earth metal. In another embodiment, the photoluminescent tag is ametal complex of a lanthanide metal. In another embodiment, thephotoluminescent tag is a chelated metal complex of a lanthanide metal.Suitable photoluminescent organometallic complexes of lanthanide metalshave been disclosed by Skotheim et al., in U.S. Pat. No. 5,128,587;Borner et al., in U.S. Pat. No. 5,756,224; Kathirgamanathan et al. in WO98/58037; and Bell et al. in EP 0744451.

IMAGING ELEMENT

The imaging element comprises at least one composition layer sensitiveto actinic radiation, that is, the layer is photosensitive. The term“photosensitive” encompass any system in which the at least onephotosensitive layer is capable of initiating a reaction or reactions,particularly photochemical reactions, upon response to actinic radiationat the first wavelength. The sensitive compositions of this inventioninclude those imaging elements in which a change in a monomer or apolymer is activated by actinic radiation, which may also be referred toas polymer imaging systems. Conventional polymer imaging systemstypically employ one of three distinct imaging reactions which arephotocrosslinking, photosolubilization, or photoinitiatedpolymerization. Photocrosslinking of a preformed polymer occurs eitherthrough dimerization of pendent reactive groups attached directly to thepolymer chain or reaction of the polymer with a separate polyfunctionalphotoactivated crosslinking agent. The resulting increase in molecularweight or network formation can produce large changes in the solubilityor in other physical properties of the polymer. Photosolubilization of apreformed polymer is brought about by the photoinitiated reaction ofeither pendent reactive groups or other molecules in the composition toincrease the solubility of the polymer. Normally little change in themolecular weight of the polymer occurs. In photoinitiated polymerizationrelatively low molecular weight monomers undergo photoinitiated cationicor free radical polymerization to form polymers. In this systemrelatively low molecular weight monomers are combined to form highermolecular weight polymers. Polymerization is generally initiated byphotoactivation of an additional low molecular weight compound known asthe photoinitiator. Polyfunctional monomers are frequently used so thathighly crosslinked networks are formed.

SENSITIVE COMPOSITIONS

The imaging element can include as the composition sensitive to actinicradiation, a sensitive composition containing at least one photoactiveor thermally active component. These include particular sensitivecompositions such as photoresists, solder masks, printing precursors,and the like, which will be further described to illustrate thisinvention. “Photoactive”, which is synonymous with “photosensitive”,describes a material which changes its chemical or physical nature, orcauses such a change, upon exposure to actinic radiation, in such a waythat the change is formed directly, e.g., an image, or that a precursor,e.g., a latent image, is formed which upon further treatment producesthe desired change. “Thermally active” describes a material whichchanges its chemical or physical nature, or causes such a change, whenits temperature is raised or when a substance is added or removed.Illustrative of such a photoactive or thermally active component is amaterial which cyclizes, dimerizes, polymerizes, crosslinks, generates afree radical, generates an ionic species or dissociates upon exposure toactinic radiation or when it is heated. Photoactive or photosensitivecomponent includes a photoinitiator, a photosensitizer or a combinationthereof; a photosolubilizer; a photodesensitizer; a photoinhibitor; aphototackifier; a photodetackifier; or a component which isphotodegradable; photochromic; photoreducible; photo-oxidizable;photoadhesive; photoreleaseable; photomagnetic; photodemagnetic;photoconductive or photoinsulative; or is a material which changes orcauses changes in refractive index upon exposure to actinic radiation.The sensitive compositions of this invention typically include thoseinstances in which the imaging element undergoes photocrosslinking orphotosolubilization reactions.

Examples of these photosensitive systems and particularly photoimagingsystems are described in “Light-Sensitive Systems: Chemistry andApplication of Nonsilver Halide Photographic Processes” by J. Kosar,John Wiley & Sons, Inc., 1965 and more recently in “Imaging ProcessesAnd Materials—Neblette's Eighth Edition” Edited by J. Sturge, V.Walworth and A. Shepp, Van Nostrand Reinhold, 1989. In such systems,actinic radiation impinges on a material containing a photoactivecomponent to induce a physical or chemical change in that material. Auseful image or latent image that can be processed into a useful imagecan thereby produced, that is, a recording element. Typically actinicradiation useful for imaging is radiation ranging from the nearultraviolet through the visible spectral regions, but in some instancesmay also include infrared, deep-ultraviolet, X-ray and electron beamradiation. Upon exposure to actinic radiation, the photoactive componentacts to change the rheological state, the solubility, the surfacecharacteristics, refractive index, the color, the electromagneticcharacteristics or other such physical or chemical characteristics ofthe photosensitive composition as described in the Neblette'spublication supra.

Typically the photosensitive compositions of this invention are used inthe form of a supported film or layer although unsupported solid objectsmay also be prepared. The photosensitive composition is applied to asuitable substrate to form a continuous film or layer thereon which isimagewise exposed to actinic radiation to form an image directly orlatent image. Alternatively, the layer may be uniformly exposed toactinic radiation to cure or harden the layer when the photosensitivecomposition is applied either in the form of a continuous or patternedlayer such as a protective finish, a paint or ink. Any conventionalsource of actinic radiation may be used including arc, discharge, andincandescent lamps as well as lasers, X-ray and electron beam units. Thelayer may be applied as a neat, solvent-free, photosensitive liquid oras a solution and dried to a solid layer wherein any conventionalcoating or printing process may be used. Alternatively, the layer orfilm may be applied by laminating a supported solid photosensitive layerto the substrate and then optionally removing the support.

Applications requiring no additional processing steps after exposure toactinic radiation, include those where an image is formed directly,e.g., photopolymer holograms as disclosed by Haugh in U.S. Pat. No.3,658,526 wherein the refractive index changes upon exposure to actinicradiation, diffusion resists by Gervay and Walker in U.S. Pat. No.3,718,473, color forming systems as by Cescon and Dessauer in U.S. Pat.No. 3,445,234 or other photochromic systems. Color forming systems basedon photooxidatizable or photoreducible agents are disclosed byMacLachlan in U.S. Pat. No. 3,390,996. Also included are thoseapplications where decorative or protective coatings are applied andphotocured or where a patterned layer is applied and photocured, e.g. aphotoresist screen printing ink as by Lipson et al. in U.S. Pat. No.4,003,877.

In those instances when a latent image is formed, the exposed orunexposed areas of the layer containing the latent image are thenmodified by removing exposed or unexposed areas, depositing a materialon or in the exposed or unexposed areas or further treating the layer todevelop an imaged layer. Exposed or unexposed areas of the layer may beremoved to form either a deep relief image or a thin stencil image withsolvent or aqueous alkaline or aqueous-based developers therefor or theymay be peeled from the complimentary unexposed or exposed areas adheredto the substrate. A deep relief image in which the sides of the reliefare tapered and do not extend to the substrate, typically is used as aletterpress or flexographic printing plate, e.g., as disclosed byPlambeck in U.S. Pat. No. 2,760,863 and Brennen and Chen in U.S. Pat.No. 4,323,637. A stencil image, in contrast, is a thin relief havingvertical side walls down to the substrate thereby forming complimentaryuncovered substrate surface areas. A stencil image has numerousapplications, e.g., as a resist as disclosed by Celeste in U.S. Pat. No.3,469,982, as a lithographic printing plate as by Alles in U.S. Pat. No.3,458,311, a photopolymer litho film as by Bratt and Cohen in U.S. Pat.No. 4,229,517, a peel-apart drafting film as by Colgrove in U.S. Pat.No. 3,353,955, or in peel-apart proofing systems as by Cohen and Fan inU.S. Pat. No. 4,247,619. When a stencil image is formed and is used as aresist, unprotected substrate areas are formed which may be furthermodified by etching the unprotected surface areas or depositing amaterial thereon. The exposed or unexposed areas of the layer containingthe latent image may be modified by depositing a material thereon suchas a photodetackification process wherein powdered material is adheredto the unexposed areas, e.g., as in the proofing process of Chu andCohen in U.S. Pat. No. 3,649,268, or a phototackification orphotoadhesive process where powdered material is adhered to the exposedareas of the layer, e.g., as in the proofing processes of Chu et al.inU.S. Pat. No. 4,243,741 and Grossa in U.S. Pat. No. 4,604,340. Liquidtoners are also used in electrostatic systems to develop latent imagesin a photoconductive or a photoinsulative process such as disclosed byRiesenfeld et al. in U.S. Pat. No. 4,732,831. Photomagnetic andphotodemagnetic systems are used to apply dye to fabrics and resists tocircuit boards as disclosed by Gorondy in U.S. Pat. No. 4,105,572, Nacciin U.S. Pat. No. 4,292,120 and Nacci et al. in U.S. Pat. Nos. 4,338,391and 4,359,516.

Photosensitive compositions containing a latent image may also bedeveloped into an image by treatment with a reagent or by furthertreatment with actinic radiation or heat. Conventional silver halide ordiazotype systems form a latent image upon exposure which is developedinto a visible image upon treatment with a developing reagent. In somesilver halide direct-writing systems, development to a visible image isaccomplished by uniform exposure to actinic radiation. In some reversalimaging processes the treatment step is used to complete the formationof the latent image before or during development. Such systems includephotopolymer systems, e.g., as disclosed by Pazos in U.S. Pat. No.4,198,242 or Dueber et al. in U.S. Pat. No. 4,477,556, containing aphotoinhibitor wherein imaging exposure generates inhibitor in theexposed areas of the layer and a subsequent uniform exposure to actinicradiation, or in some instances uniformly heated, generates a latentimage in the complimentary areas free of photogenerated inhibitor. Suchreversal systems also include photodesensitizable systems, e.g., asdisclosed by Roos in U.S. Pat. No. 3,778,270, wherein, in the exposedareas, a component required for image or latent image formation isdegraded or desensitized to an inactive form and the component in theunexposed areas is developed into an image or latent image by subsequenttreatment with a reagent.

Illustrative of such photosensitive systems are those described inChapter 7, “Polymer Imaging” by A. B. Cohen and P. Walker in Neblette'ssupra, pages 226-262, in which photocrosslinking, photodimerization,photocyclization, photosolubilization, and both ionic and free radicalphotopolymerization, as well as electrostatic photopolymer imaging andsolid imaging are discussed. In Chapter 8, “Low Amplification ImagingSystems” by R. Dessauer and C. E. Looney, pages 263-278, imaging systemsdiscussed include color forming free radical, diazo, and vesicularsystems, photochromism, phototackification and photodetackification aswell as thermal and photothermal systems.

PHOTOPOLYMERIZABLE COMPOSITIONS

The imaging element can include as the composition sensitive to actinicradiation a photopolymerizable composition that contains anethylenically unsaturated compound and a photoinitiator orphotoinitiator system. The ethylenically unsaturated compound may alsobe referred to as monomeric material or monomer. In such systemsgenerally a polymer is present which functions as a dispersiblepolymeric binder component to impart desired physical and chemicalcharacteristics to the exposed and unexposed photopolymerizablecomposition. Upon exposure to actinic radiation, the photoinitiatorsystem induces chain propagated polymerization of the monomeric materialby either a condensation mechanism or by free radical additionpolymerization. While all photopolymerizable mechanisms arecontemplated, the compositions and processes of this invention will bedescribed in the context of free radical initiated additionpolymerization of monomers having one or more terminal ethylenicallyunsaturated groups. In this context, the photoinitiator system whenexposed to actinic radiation acts as a source of free radicals needed toinitiate polymerization of the monomer. The photoinitiator of the systemmay be activated by a photosensitizer which absorbs actinic radiationwhich may be outside the absorption spectrum of the initiator itself, tosensitize the addition polymerization in more practical radiationspectral regions such as near ultraviolet, visible light and nearinfrared. In the narrow sense, the term photoactive component of thecompositions of this invention refers to the material which absorbs theactinic radiation, e.g., the photoinitiator or the photosensitizer, butin the broader sense the term photoactive component refers to any or allthe essential materials needed for photopolymerization, i.e., thephotoinitiating system and the monomer.

Photopolymerizable compositions contain an initiating system activatedby actinic radiation and at least one ethylenically unsaturated compoundcapable of forming a high polymer by photoinitiated additionpolymerization. Although photopolymerizable compositions having only theinitiating system and the at least one ethylenically unsaturatedcompound will react to actinic radiation, typically in commercial usethese compositions also include the polymeric binder component.Typically the at least one ethylenically unsaturated compound isnongaseous and has a boiling point above 100° C. at normal atmosphericpressure. In one embodiment the photopolymerizable compositions containmonofunctional or polyfunctional acrylates or methacrylates, andparticularly preferred are such compositions containing monomers withtwo, three or more acrylate or methacrylate groups to allow concurrentcrosslinking during the photopolymerization process. As such, the term“photopolymerizable” is intended to encompass systems that arephotopolymerizable, photocrosslinkable, or both.

ADDITION POLYMERIZABLE MONOMERS

Monomers that can be used in the composition activated by actinicradiation are well known in the art, and include, but are not limitedto, addition-polymerization ethylenically unsaturated compounds havingrelatively low molecular weights that is, molecular weights generallyless than about 30,000, and preferably less than about 5000. Unlessdescribed otherwise in the specification, the molecular weight is theweighted average molecular weight. The addition polymerization compoundmay also be an oligomer, and can be a single or a mixture of oligomers.If a polyacrylol oligomer is used, the oligomer should preferably have amolecular weight greater than 1000. The composition can contain a singlemonomer or a combination of monomers. The monomer compound capable ofaddition polymerization is present in at least an amount of 5%,preferably 10 to 20%, by weight of the composition.

Suitable monomers include, but are not limited to, acrylate monoestersof alcohols and polyols; acrylate polyesters of alcohols and polyols;methacrylate monoesters of alcohols and polyols; and methacrylatepolyesters of alcohols and polyols; where the alcohols and the polyolssuitable include alkanols, alkylene glycols, trimethylol propane,ethoxylated trimethylol propane, pentaerythritol, and polyacrylololigomers. Other suitable monomers include acrylate derivatives andmethacrylate derivatives of isocyanates, esters, epoxides, and the like.A combination of monofunctional and multifunctional acrylates ormethacrylates may be used.

Examples of suitable monomers include the following: t-butyl acrylate,hexanediol diacrylate, hexanediol dimethyacrylate, 1,5-pentanedioldiacrylate, N,N-diethylaminoethyl acrylate, ethylene glycol diacrylate,1,4-butanediol diacrylate, diethylene glycol diacrylate, hexamethyleneglycol diacrylate, 1,3-propanediol diacrylate, decamethylene glycoldiacrylate, decamethylene glycol dimethacrylate, 1,4-cyclohexanedioldiacrylate, 2,2-dimethylolpropane diacrylate, glycerol diacrylate,tripropylene glycol diacrylate, glycerol triacrylate, trimethylolpropanetriacrylate, pentaerythritol triacrylate, polyoxyethylatedtrimethylolpropane triacrylate and trimethacrylate and similar compoundsas disclosed in U.S. Pat. No. 3,380,831, 2,2-di(p-hydroxyphenyl)-propanediacrylate, pentaerythritol tetraacrylate,2,2-di-(p-hydroxyphenyl)-propane dimethacrylate, triethylene glycoldiacrylate, polyoxyethyl-2,2-di-(p-hydroxyphenyl)-propanedimethacrylate, di-(3-methacryloxy-2-hydroxypropyl)ether of bisphenol-A,di-(2-methacryloxyethyl) ether of bisphenol-A,di-(3-acryloxy-2-hydroxypropyl) ether of bisphenol-A,di-(2-acryloxyethyl) ether of bisphenol-A,di-(3-methacryloxy-2-hydroxypropyl) ether of tetrachloro-bisphenol-A,di-(2-methacryloxyethyl) ether of tetrachloro-bisphenol-A,di-(3-methacryloxy-2-hydroxypropyl) ether of tetrabromo-bisphenol-A,di-(2-methacryloxyethyl) ether of tetrabromo-bisphenol-A,di-(3-methacryloxy-2-hydroxypropyl) ether of 1,4-butanediol,di-(3-methacryloxy-2-hydroxypropyl) ether of diphenolic acid,triethylene glycol dimethacrylate, polyoxypropyl one trimethylol propanetriacrylate (462), ethylene glycol dimethacrylate, butylene glycoldimethacrylate, 1,3-propanediol dimethacrylate, 1,2,4-butanetrioltrimethacrylate, 2,2,4-trimethyl-1,3- pentanediol dimethacrylate,pentaerythritol trimethacrylate, I-phenyl ethylene-1,2-dimethacrylate,pentaerythritol tetramethacrylate, trimethylol propane trimethacrylate,1,5-pentanediol dimethacrylate, diallyl fumarate, 1,4-benzenedioldimethacrylate, 1,4-diisopropenyl benzene, and 1,3,5-triisopropenylbenzene.

Other examples of suitable monomers include acrylate and methacrylatederivatives of isocyanates, esters, epoxides and the like. In someend-use imaging systems it may be desirable to use monomer that provideelastomeric properties to the element. Examples of elastomeric monomersinclude, but are not limited to, acrylated liquid polyisoprenes,acrylated liquid butadienes, liquid polyisoprenes with high vinylcontent, and liquid polybutadienes with high vinyl content, (that is,content of 1-2 vinyl groups is greater than about 20% by weight).

A class of monomers are an alkylene or a polyalkylene glycol diacrylateprepared from an alkylene glycol of 2 to 15 carbons or a polyalkyleneether glycol of 1 to 10 ether linkages, and those disclosed in U.S. Pat.No. 2,927,024, e.g., those having a plurality of addition polymerizableethylenic linkages particularly when present as terminal linkages. Thoseclass of monomers wherein at least one and preferably most of suchlinkages are conjugated with a double bonded carbon, including carbondouble bonded to carbon and to such heteroatoms as nitrogen, oxygen andsulfur, are suitable in one embodiment. Also preferred are suchmaterials wherein the ethylenically unsaturated groups, especially thevinylidene groups, are conjugated with ester or amide structures.

Further examples of monomers can be found in Chen U.S. Pat. No.4,323,636; Fryd et al., U.S. Pat. No. 4,753,865; Fryd et al., U.S. Pat.No. 4,726,877 and Feinberg et al., U.S. Pat. No. 4,894,315.

PHOTOINITIATOR SYSTEMS

The photoinitiator can be any single compound or combination ofcompounds (that is, a photoinitiator system) which is sensitive toactinic radiation, generating free radicals which initiate thepolymerization of the monomer or monomers without excessive termination.The photoinitiator system has one or more compounds that directlyfurnish free-radicals when activated by actinic radiation. The systemalso may contain a sensitizer that is activated by the actinicradiation, causing the compound to furnish the free-radicals. Usefulphotoinitiator systems typically will contain a sensitizer that extendsspectral response into the near ultraviolet, visible, and near infraredspectral regions. Preferably, the photoinitiator is sensitive to actinicradiation in the ultraviolet and/or visible wavelengths of radiation.Photoinitiators are generally present in amounts from 0.001% to 10.0%based on the weight of the photopolymerizable composition.

Any of the known classes of photoinitiators, particularly free radicalphotoinitiators such as quinones, benzophenones, benzoin ethers, arylketones, peroxides, biimidazoles, benzyl dimethyl ketal, hydroxyl alkylphenyl acetophone, dialkoxy actophenone, trimethylbenzoyl phosphineoxide derivatives, aminoketones, benzoyl cyclohexanol, methyl thiophenyl morpholino ketones, morpholino phenyl amino ketones, alphahalogennoacetophenones, oxysulfonyl ketones, sulfonyl ketones,oxysulfonyl ketones, sulfonyl ketones, benzoyl oxime esters,thioxanthrones, camphorquinones, ketocouumarins, and Michler's ketonemay be used.

A large number of free-radical generating compounds, including redoxsystems such as Rose Bengal/2-dibutylaminethanol, may be selected toadvantage. Photoreducible dyes and reducing agents such as thosedisclosed in U.S. Pat. Nos. 2,850,445; 2,875,047; 3,097,096; 3,074,974;3,097,097; 3,145,104; and 3,579,339; as well as dyes of the phenazine,oxazine, and quinone classes; ketones, quinones;2,4,5-triphenylimidazolyl dimers with hydrogen donors, and mixturesthereof as described in U.S. Pat. Nos. 3,427,161; 3,479,185; 3,549,367;4,311,783; 4,622,286; and 3,784,557 can be used as initiators. Otherinitiators are dye-borate complexes disclosed in U.S. Pat. No.4,772,541; and trichloromethyl triazines disclosed in U.S. Pat. Nos.4,772,534 and 4,774,163. A useful discussion of dye sensitizedphotopolymerization can be found in “Dye Sensitized Photopolymerization”by D. F. Eaton in Adv. in Photochemistry, Vol. 13, D. H. Volman, G. S.Hammond, and K. Gollinick, eds., Wiley-Interscience, New York, 1986, pp.427-487. Similarly, the cyclohexadienone compounds of U.S. Pat. No.4,341,860 are useful as initiators.

In one embodiment suitable photoinitiators include CDM-HABI, i.e.,1H-Imidazole,2-(2-chlorophenyl)-1-[2-(-chlorophenyl-4,5-di(3-methoxyphenyl)-2H-imidazol-2-yl)]-4,5-di(3-methoxyphenyl)-;o-CI-HABI, i.e., 1H-Imidazole,2-(2-chlorophenyl)-1-[2-(2-chlorophenyl-4,5-diphenyl-2H-imidazol-2-yl)]-4,5-diphenyl-;and TCTM-HABI, i.e., 1H-Imidazole,2-(2-chlorophenyl)-1-[2-(2-chlorophenyl)-4-(3,4-dimethoxyphenyl)-5-phenyl)-2H-imidazol-2-yl)]-4-(3,4-dimethoxyphenyl)-5-(phenyl)-;each of which is typically used with a hydrogen donor.

Sensitizers useful with photoinitiators include methylene blue and thosedisclosed in U.S. Pat. Nos. 3,554,753; 3,563,750; 3,563,751; 3,647,467;3,652,275; 4,162,162; 4,268,667; 4,351,893; 4,454,218; 4,535,052; and4,565,769. A preferred group of sensitizers include thebis(p-dialkylaminobenzylidene) ketones disclosed in Baum et al. U.S.Pat. No. 3,652,275, and the arylyidene aryl ketones disclosed in DueberU.S. Pat. No. 4,162,162. In one embodiment suitable sensitizers includethe following: DBC, i.e., cyclopentanone;2,5-bis-{[4-(diethylamino)-2-methylphenyll-methylenel; DEAW, i.e.,cyclopentanone, 2,5-bisf[4-(diethylamino)-phenyllmethylenel;dimethoxy-JDI, i.e., IH-inden-I-one,2,3-dihydro-5,6-dimethoxy-2-[(2,3,6,7-tetrahydro-IH,5H-benzo[i,j]-quinolizin-9-yl)methylene)-;and JAW, i.e., cyclopentanone,2,5-bis[(2,3,6,7-tetrahydro-IH,5H-benzo[i,j]quinolizin-1-yl)methylene].Other particularly useful sensitizers are cyclopentanone,2,5-bis[2-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene) ethylidene],CAS 27713-85-5; and cyclopentanone,2,5-bis[2-(I-ethylnaphtho[1,2-d]thiazol-2(IH)-ylidene)ethylidenel, CAS27714-25-6.

Hydrogen donor compounds that function as chain transfer agents in thephotopolymer compositions include: 2-mercaptobenzoxazole,2-mercaptobenzothiazole, 4-methyl-4H-1,2,4-triazole-3-thiol, etc.; aswell as various types of compounds, e.g., (a) ethers, (b) esters, (c)alcohols, (d) compounds containing allylic or benzylic hydrogen, (e)acetals, (f) aldehydes, and (g) amides disclosed in column 12, lines 18to 58 of MacLachlan U.S. Pat. No. 3,390,996. Suitable hydrogen donorcompounds for use in systems containing both biimidazole type initiatorand N-vinyl carbazole are 5-chloro-2-mercaptobenzothiazole;2-mercaptobenzothiazole; 1H-Ir2,4-triazole-3-thiol;6-ethoxy-2-mercaptobenzothiazole; 4-methyl-4H-1,2,4-triazole-3-thiol;1-dodecanethiol; and mixtures thereof.

A particularly preferred class of photoinitiators and photosensitizersare benzophenone, Michler's ketone, ethyl Michler's ketone,p-dialkylaminobenzaldehydes, p-dialkylaminobenzoate alkyl esters,polynuclear quinones, thioxanthones, hexaarylbiimidazoles,cyclohexadienones, benzoin, benzoin dialkyl ethers, or combinationsthereof where alkyl contains 1 to 4 carbon atoms.

POLYMERIC BINDER

Generally a photosensitive composition contains a polymer in addition tothe one or more photoactive components. The polymer may be photoactiveitself or may act as a matrix for the one or more photoactivecomponents. The polymer is typically, but not necessarily, preformed.The polymer is not limited and includes polymers that are linear,branched, radial, comb, and can become interpenetrating networks. Othercomponents in the composition should be compatible with the binder tothe extent that a clear, non-cloudy photosensitive layer is produced.

The photopolymerizable composition may include a binder that is apreformed polymer that serves as a matrix for the monomer andphotoinitiator system prior to exposure. The binder is a majorcontributor to the physical properties of the photopolymer, both beforeand after exposure. Addition of the binder allows the imaging element tobe manufactured and handled as a dry film. As is the case withphotoinitiators and monomers, the selection criteria for binders varywith the application. Molecular weight, glass transition temperature,flexibility, chemical resistance, solubility, toughness, and tensilestrength, as well as cost and availability are among the factors thatgovern binder selection. The binder should be of sufficient molecularweight and have sufficiently high glass transition temperature that afilm is formed when the composition is coated. Suitable binders can havewidely varying molecular weights, from as low as 25,000 to greater than300,000, to as much as 1,200,000 have been described. Unless otherwiseindicated the molecular weight of the polymeric binder is a meanmolecular weight Mw determined with the aid of gel permeationchromatography using polystyrene standards.

The binder can be a single polymer or mixture of polymers. The bindercan be thermoplastic, elastomeric, or a thermoplastic elastomer. Bindersinclude natural or synthetic polymers of conjugated diolefinhydrocarbons, including polyisoprene, 1,2-polybutadiene,1,4-polybutadiene, and butadiene/acrylonitrile. In one embodiment, thethermoplastic binder is an elastomeric block copolymer of an A-B-A typeblock copolymer, where A represents a non-elastomeric block, preferablya vinyl polymer and most preferably polystyrene, and B represents anelastomeric block, preferably polybutadiene or polyisoprene. The blockcopolymers can be linear block copolymers, radial block copolymers, orquasi-radial block copolymers. The are usually three-block copolymers ofthe A-B-A type, but can also be two block copolymers of the A-B type orthose comprising a plurality of alternating elastomeric andthermoplastic blocks, for example A-B-A-B-A. Suitable thermoplasticelastomeric binders of this type include poly(styrene/isoprene/styrene)block copolymers and poly(styrene/butadiene/styrene) block copolymerswhich are preferred. The non-elastomer to elastomer ratio is preferablyin the range of from 10:90 to 35:65. In one embodiment, the binder ispresent in an amount of at least 55% by weight of the photosensitivelayer for photosensitive elements useful as flexographic printing forms.

The term binder, as used herein, encompasses core shell microgels andblends of microgels and preformed macromolecular polymers, such as thosedisclosed in Fryd et al., U.S. Pat. No. 4,956,252 and Quinn et al., U.S.Pat. No. 5,707,773.

Other suitable photosensitive elastomers that may be used includepolyurethane elastomers. An example of a suitable polyurethane elastomeris the reaction product of (i) an organic diisocyanate, (ii) at leastone chain extending agent having at least two free hydrogen groupscapable of polymerizing with isocyanate groups and having at least oneethylenically unsaturated addition polymerizable group per molecule, and(iii) an organic polyol with a minimum molecular weight of 500 and atleast two free hydrogen containing groups capable of polymerizing withisocyanate groups. For a more complete description of some of thesematerials see U.S. Pat. No. 5,015,556.

POLYMERIC MODIFIERS

The photopolymerizable composition may contain a second polymeric binderto modify adhesion, flexibility, hardness, oxygen permeability, moisturesensitivity and other mechanical or chemical properties required duringits processing or end use.

Suitable polymeric binders that can be used in combination include:polyacrylate and alpha-alkyl polyacrylate esters, e.g., polymethylmethacrylate and polyethyl methacrylate; polyvinyl esters, e.g.,polyvinyl acetate, polyvinyl acetate/acrylate, polyvinylacetate/methacrylate and hydrolyzed polyvinyl acetate; ethylene/vinylacetate copolymers; polystyrene polymers and copolymers, e.g., withmaleic anhydride and esters; vinylidene chloride copolymers, e.g.,vinylidene chloride/acrylonitrile; vinylidene chloride/methacrylate andvinylidene chloride/vinyl acetate copolymers; polyvinyl chloride andcopolymers, e.g., poly(vinyl chloride/vinyl acetate); polyvinylpyrrolidone and copolymers, e.g., poly(vinyl pyrrolidone/vinyl acetate)saturated and unsaturated polyurethanes; synthetic rubbers, e.g.,butadiene/acrylonitrile, acrylonitrile/butadiene/styrene,methacrylate/acrylonitrile/butadiene/styrene copolymers,2-chlorobutadiene-1,3 polymers, chlorinated rubber, andstyrene/butadiene/styrene, styrene/isoprene/styrene block copolymers;high molecular weight polyethylene oxides of polyglycols having averagemolecular weights from about 4,000 to 1,000,000; epoxides, copolyesters,e.g., those prepared from the reaction product of a polymethylene glycolof the formula HO(CH₂)_(n)OH, where n is a whole number 2 to 10inclusive, and (1) hexahydroterephthalic, sebacic and terephthalicacids, (2) terephthalic, isophthalic and sebacic acids, (3) terephthalicand sebacic acids, (4) terephthalic and isophthalic acids, and (5)mixtures of copolyesters prepared from said glycols and (i)terephthalic, isophthalic and sebacic acids and (ii) terephthalic,isophthalic, sebacic and adipic acid; nylons or polyamides, e.g.,N-methoxymethyl polyhexamethylene adipamide; cellulose esters, e.g.,cellulose acetate, cellulose acetate succinate and cellulose acetatebutyrate; cellulose ethers, e.g., methyl cellulose, ethyl cellulose andbenzyl cellulose; polycarbonates; polyvinyl acetal, e.g., polyvinylbutyral, polyvinyl formal; polyformaldehydes.

In the case where aqueous development of the photosensitive compositionis desirable, the branched polymer product and/or the binder shouldcontain sufficient acidic or other groups to render the compositionprocessible in aqueous developer. Useful aqueous-processible bindersinclude those disclosed in U.S. Pat. No. 3,458,311; U.S. Pat. No.4,273,857; U.S. Pat. No. 6,210,854; U.S. Pat. No. 5,679,485; U.S. Pat.No. 6,025,098; U.S. Pat. No. 5,830,621; U.S. Pat. No. 5,863,704; andU.S. Pat. No. 5,889,116. Useful amphoteric polymers includeinterpolymers derived from N-alkylacrylamides or methacrylamides, acidicfilm-forming comonomer and an alkyl or hydroxyalkyl acrylate such asthose disclosed in U.S. Pat. No. 4,293,635. In one embodiment, foraqueous development the photosensitive layer will be removed in portionswhich are not exposed to radiation but will be substantially unaffectedduring development by a liquid such as wholly aqueous solutionscontaining 1% sodium carbonate by weight.

PLASTICIZERS

The photopolymerizable compositions may also contain a plasticizer tomodify adhesion, flexibility, hardness, solubility, film-formingproperties, and other mechanical or chemical properties required duringits processing or end use. Suitable plasticizers include triethyleneglycol, triethylene glycol diacetate, triethylene glycol dipropionate,triethylene glycol dicaprylate, triethylene glycol dimethyl ether,triethylene glycol bis(2-ethylhexanoate), tetraethylene glycoldiheptanoate, poly(ethylene glycol), poly(ethylene glycol) methyl ether,isopropylnaphthalene, diisopropylnaphthalene, poly(propylene glycol),glyceryl tributyrate, diethyl adipate, diethyl sebacate, dibutylsuberate, dioctyl phthalate, tricresyl phosphate, tributyl phosphate,tris(2-ethylhexyl) phosphate, Brij® 30 [C₁₂H₂₅(OCH₂CH₂)₄₀OH, and Brij®35 [C₁₂H₂₅(OCH₂CH₂)₂₀OH].

Other examples of suitable plasticizers include modified or unmodifiednatural oils and resins; paraffinic mineral oils; alkyl, alkenyl,arylalkyl or arylalkenyl esters of acids, such as alkanoic acids orarylcarboxylic acids; aliphatic hydrocarbon oils, e.g., naphthenic andparaffinic oils; liquid polydienes, e.g., liquid polybutadiene, andliquid polyisoprene; and liquid oligomeric acrylonitrile-butadienecopolymers. Generally, plasticizers are liquids having molecular weightsof less than about 5000, but can have molecular weights up to about30,000. Plasticizers having low molecular weight will encompassmolecular weights less than about 30,000. In one embodiment, theplasticizer is present from 5 to 40% by weight, based upon thecomposition.

OPTIONAL COMPONENTS

Other compounds conventionally added to photopolymer compositions canalso be present to modify the physical properties of the film for aparticular use. Such components include: other polymeric binders,fillers, thermal stabilizers, hydrogen donors, thermal crosslinkingagents, ultraviolet radiation materials, adhesion modifiers, coatingaids, and release agents.

CROSSLINKING AGENTS

When the photopolymerizable composition is to be used as a permanentcoating, such as a solder mask, a chemically or thermally activatedcrosslinking agent may be incorporated to improve high temperaturecharacteristics, chemical resistance or other mechanical or chemicalproperties required in the end-use product. Suitable crosslinking agentsinclude those disclosed by Gervay in U.S. Pat. No. 4,621,043 andGeissler et al. in U.S. Pat. No. 4,438,189, such as melamines, ureas,benzoguanamines and the like. Examples of suitable crosslinkingcompounds include: N-Methylol compounds of organic carboxamides; andC-methylol compounds of phenols, phenol-ethers and aromatichydrocarbons. Instead of the aforementioned methylol compounds, it isalso possible to use, for example, the corresponding methyl, ethyl orbutyl ethers, or esters of acetic acid or propionic acid. A preferredcrosslinking agent of this class is hexamethoxymethyl melamine.

Also useful as crosslinking agents are compounds containing two or moreepoxy groups such as the bis-epoxides disclosed by Herwig et al. in U.S.Pat. No. 4,485,166. Bis-glycidyl ethers of trihydric alcohols, such asglycerol, or of halogenated bisphenol A, can also be used. Preferredcrosslinking agents of this class are2,2-bis-(4-glycidoxy-phenyl)-propane, 2,2-bis-(4-215epoxyethoxy-phenyl)-propane, bis-glycidyl ether oftetra-chloro-bisphenol A, bis-glycidyl ether of tetra-bromo-bisphenol A,bis-oxiranyl ether of tetra-chloro-bisphenol A, and bis-oxiranyl etherof tetra-bromo-bisphenol A.

Also useful as crosslinking agents are blocked polyisocyanates. Uponheating the blocked polyisocyanate, the blocking groups split off toyield the free reactive polyisocyanate. Useful polyisocyanates includetoluene diisocyanate; isophorone diisocyanate; 1,4-naphthalenediisocyanate; 1,6-hexamethylene diisocyanate; tetramethyl xylenediisocyanate; bis(4-isocyanatocyclohexyl)methane and the like. Usefulblocking groups are derived from caprolactam; diethyl malonate;alcohols; phenols; oximes, e.g., methyl ethyl ketoxime; and the like.

ADHESION PROMOTER

When the photopolymerizable composition is to be used as a coating on ametal surface, such as a photoresist, a heterocyclic or mercaptancompound may be added to improve adhesion of the coating to the metalrequired during processing or in the end-use product. Suitable adhesionpromoters include heterocyclics such as those disclosed by Hurley et al.in U.S. Pat. No. 3,622,334, Jones in U.S. Pat. No. 3,645,772, and Weedin U.S. Pat. No. 4,710,262. Preferred adhesion promoters for use inphotoresists and solder masks include benzotriazole,5-chloro-benzotriazole, 1-chloro-benzotriazole, 1-carboxy-benzotriazole,1-hydroxy-benzotriazole, 2-mercaptobenzoxazole,1H-1,2,4-triazole-3-thiol, 5-amino-1,3,4-thiodiazole-2-thiol, andmercaptobenzimidazole.

OTHER COMPONENTS

The photopolymerizable compositions may contain other components such asthermal polymerization inhibitors, processing aids, antioxidants,antiozonants, dyes and pigments, optical brighteners and the like tostabilize, color or otherwise enhance the composition.

Thermal polymerization inhibitors that can be used in thephotopolymerizable compositions are: p-methoxyphenol, hydroquinone, andalkyl and aryl-substituted hydroquinones and quinones, tert-butylcatechol, pyrogallol, copper resinate, naphthylamines, beta-naphthol,cuprous chloride, 2,6-di-tert-butyl-p-cresol, phenothiazine, pyridine,nitrobenzene and dinitrobenzene, p-toluquinone and chloranil. Alsouseful for thermal polymerization inhibitors are the nitrosocompositions disclosed in U.S. Pat. No. 4,168,982.

Dyes and pigments are not limited however, any colorant used shouldpreferably be transparent to the actinic radiation used.

Useful optical brighteners include those disclosed by Held in U.S. Pat.No. 3,854,950. Ultraviolet radiation absorbing materials useful in theinvention are also disclosed by Held in U.S. Pat. No. 3,854,950. Opticalbrighteners are not encompassed within the photoluminescent tag of thepresent invention.

Processing aids may be such things as low molecular weight polymerscompatible with the elastomeric block copolymer, such as low molecularweight alpha-methylstyrene polymer or copolymer. Antiozonants includehydrocarbon waxes, norbornenes, and vegetable oils. Suitableantioxidants include alkylated phenols, alkylated bisphenols,polymerized trimethyldihydroquinone, and dilauryl thiopropinoate.

Photoresist Applications

The imaging elements of this invention are useful as photoresists forpreparing printed circuit boards. In general the use of resists toprepare printed circuits is described in “Printed Circuits Handbook”,Second Edition, edited by C. F. Coombs, Jr, published by McGraw-Hill,Inc. in 1979 which includes both screen printed resists as well asphotoresists. The use of conventional photoresists for preparingphotocircuits is described in “Photoresist - Materials And Processes”,by W. S. DeForest, published by McGraw-Hill, Inc. in 1975 which includesnegative working photopolymerizable and photocrosslinkable ordimerizable systems as well as positive working photosolubilizablesystems. Photoresists may be used in temporary coatings in a primaryimaging process to make the printed circuit or they may be used in asecondary imaging process to make permanent coatings, e.g., a soldermask, to protect the circuit during subsequent processing or fromenvironmental effects during use. Permanent coatings also are used asintermediate insulative layers in the manufacture of multilayer printedcircuits.

Prepress Proof Applications

The imaging elements of the present invention are useful as prepressproofs for preparing images from a multicolor original that will berepresentative of the printed image on-press. Proofing is a processwhich uses color separations to create a colored image called a proof tovisualize what the final printed image will look like typically withoutactually making printing plates and running the printing press. Prepressproofs, which may also be referred to as off-press proofs or pre-plateproofs, are usually made by photochemical or photomechanical processes.These proofing systems generally make proofs by exposing photosensitiveelement to actinic radiation through one of the image bearing colorseparation transparencies to produce a duplicate image that is either apositive or a negative of the transparency depending on the elementused. The radiation may make soluble areas insoluble, insoluble areassoluble, tacky areas nontacky, or nontacky areas tacky depending on theelement used. After imagewise exposure, the photosensitive element canbe developed by removing nonimagable areas, e.g., by washing out solubleareas. The tacky areas of the element may have to be toned with a dry orliquid colorant. Alternatively, the colorant may be incorporated intothe imaging element. This process is repeated for all color separations.Then the processed elements are laminated together one at a timesometimes on a support or substrate. Protective layers may be peeledapart and removed from the element before they are laminated to thesupport or other image elements. Finally, the color images may betransferred from the support to a receptor, transfer or display sheet,such as a sheet of paper, to form the final proof.

Known methods of color proofing (prepress proofing) which use aphotopolymer include an overlay method and a surprint method. In theoverlay method, plural sheets having separation images of differentcolor formed on transparent supports are prepared and then placed uponone another to conduct color proofing. In the surprint method, amulticolor image is obtained by successively forming separation imagesof different color on a single support.

In the overlay method, each color separation can be printed on atransparent supporter coated with colored sensitizer for every color andeach color is superposed on a white sheet to perform the proofreading(U.S. Pat. No. 3,136,637; U.S. Pat. No. 3,221,553; U.S. Pat. No.3,326,682; U.S. Pat. No. 4,282,308; U.S. Pat. No. 4,286,043; and EP 385466, and exemplified by the DuPont “Cromacheck” system). This methodallows rapid proof-making and can be utilized for preparing acolor-separated proof by properly combining two or three colors.

The surprint method is disclosed, e.g., in U.S. Pat. Nos. 3,060,023,3,060,024; 3,060,025; 3,060,026; 4,489,153; and EP 385 466 in which aplurality of images formed on the photosensitive layers according toimages of separated colors are transferred to a single image receptorone after another to form a prepress proof. Each of the photosensitivelayers may be colored with a color equivalent to the separated color ofan image, or a transferred image may be colored with correspondingpowder color toners.

Classes of photomechanical transfer that use heat derived fromirradiation rather than photopolymerization are termed thermal transferimaging and include dye diffusion or sublimation, thermal mass transferand melt transfer.

In dye diffusion or sublimation, dyes are caused to migrate from a donorto a receptor in amounts proportional to the energy applied, givingcontinuous tone images, as in U.S. Pat. No. 5,034,371. In thermal masstransfer, zero or 100% transfer of the transfer layer takes placeaccording to whether the applied energy exceeds a given level. Thermalmass transfer is highly suited to half tone reproduction since theresulting images consist of areas of zero or maximum optical density.

WO 88/04237 discloses a melt transfer thermal imaging medium which islaser-addressable, comprising a support sheet having a surface of amaterial which may be temporarily liquefied by heat and upon which isdeposited a particulate or porous layer of an image forming substancewhich is wettable by the material in its liquefied state. Either theimage forming substance is itself IR-absorbing, or a separate absorberis present. In exposed areas, the liquefiable material melts, wets theparticles of the image forming substance, then resolidifies, thusanchoring the particles to the substrate. Removal of a stripping sheet(either present from the outset or applied subsequent to exposure) thencauses selective removal of the particles in the non-exposed areas.

Also suitable are laser induced thermal mass transfer imaging processesand products which utilize a receiver element that are described in U.S.Pat. No. 6,294,308 of Caspar, et al., U.S. Pat. No. 5,834,154, ofYamazaki et al., U.S. Pat. No. 6,316,385 of Usuki, et al. and U.S. Pat.No. 6,294,308.

At least two modes of address may be distinguished for thermal transferimaging, namely print head and infrared (IR) address. In the former,heat is typically supplied to the donor-receptor assembly via anexternal print head comprising an array of microresistors, while in thelatter the energy is typically supplied by a radiant source (usually anIR emitter such as a laser) and converted to heat within thedonor-receptor assembly by a suitably-placed radiation absorber. Theseprocesses have been described in, for example, Baldock, U.K. Patent2,083,726; DeBoer, U.S. Pat. No. 4,942,141; Kellogg, U.S. Pat. No.5,019,549; Evans, U.S. Pat. No. 4,948,776; Foley et al., U.S. Pat. No.5,156,938; Ellis et al., U.S. Pat. No. 5,171,650; and Koshizuka et al.,U.S. Pat. No. 4,643,917.

These proofing methods are also well-known imaging processes that can beused in applications such as electronic circuit manufacture, colorfilters, display manufacture, lithography, and other areas.

Printing Form Applications

The imaging elements of this invention are useful as printing forms forrelief printing, such as flexographic and letterpress printing, andlithographic printing. In general printing forms for use in printing andprinting processes are described in Chapters 7 and 16 of “ImagingProcesses And Material—Neblette's Eight Edition” edited by J. Sturge, V.Walworth and A. Shepp, Van Nostrand Reinhold, 1989, and in “Pocket Pal AGraphic Arts Production Handbook” edited by M. H. Bruno, InternationalPaper Company, 15^(th) edition, 1994.

A preferred use for the imaging elements of the present invention is forrelief printing forms, particularly flexographic printing forms.Flexographic printing processes and printing forms are described in“Flexography Principles And Practices” Foundation of FlexographicTechnical Association, Inc., 4^(th) edition, 1991. Flexographic printingplates are widely used for printing of packaging materials ranging fromcorrugated carton boxes to card boxes and to continuous web of plasticfilms. Flexographic printing plates can be prepared fromphotopolymerizable compositions, such as those described in U.S. Pat.Nos. 4,323,637 and 4,427,759. The photopolymerizable compositionsgenerally comprise an elastomeric binder, at least one monomer and aphotoinitiator. Photosensitive elements generally have a layer of thephotopolymerizable composition interposed between a support and acoversheet or a multilayer cover element. The thickness of thephotopolymerizable layer can vary over a wide range depending upon thetype of printing plate desired, for example, from about 0.010 inches toabout 0.250 inches or greater (about 0.025 cm to about 0.64 cm orgreater). For so-called “thin plates” typically the photopolymerizationlayer can range from about 0.010 inches to about 0.067 inches (about0.025 cm to about 0.17 cm) in thickness.

The photopolymerizable layer itself can be prepared in many ways byadmixing the binder, monomer, initiator, and other ingredients. It ispreferred that the photopolymerizable mixture be formed into a hot meltand then calendered to the desired thickness. An extruder can be used toperform the functions of melting, mixing, deaerating and filtering thecomposition. In one embodiment, the photoluminescent tag is added at anearly stage of the extrusion process to assure that the tag is uniformlydispersed in the photosensitive composition. The extruded mixture isthen calendered between the support and the temporary coversheet.Alternatively, the photopolymerizable material can be placed between thesupport and the temporary coversheet in a mold. The layers of materialare then pressed flat by the application of heat and/or pressure.

Although a photosensitive printing element is typically used in sheetform, there are particular applications and advantages to using theprinting element in a continuous cylindrical form. A continuous printingelement has applications in the flexographic printing of continuousdesigns used in wallpaper, decoration and gift wrapping paper, andtight-fit conditions for registration, since the designs can be easilyprinted without print-through of the plate seam. Furthermore, such acontinuous printing element is well-suited for mounting on laserexposure equipment where it can replace the drum or be mounted on thedrum for exposure by a laser to achieve precise registration.

The formation of a seamless, continuous printing element can beaccomplished by several methods. The photopolymerizable flat sheetelement can be reprocessed by wrapping the element around a cylindricalform, usually a printing sleeve or the printing cylinder itself, andfusing or joining the edges together to form a seamless, continuouselement. Processes for joining the edges of a plate into a cylindricalform have been disclosed, for example, in German patent DE 28 44 426,United Kingdom patent GB 1 579 817, European patent application EP 0 469375, U.S. Pat. No. 4,883,742, and U.S. Pat. No. 4,871,650. Cylindricalseamless photopolymerizable elements may also be prepared according tothe method and apparatus disclosed by Cushner et al. in U.S. Pat. No.5,798,019.

Flexographic printing plates are characterized by their ability tocrosslink or cure upon exposure to actinic radiation. Typically theplate is uniformly exposed through the backside of the plate to aspecified amount of actinic radiation. Next, an imagewise exposure ofthe front-side of the plate is made through an image-bearing artwork ora template, such as a photographic negative or transparency (e.g. silverhalide film) or through an in-situ mask having radiation opaque areasthat had been previously formed above the photopolymerizable layer. Theplate is exposed to actinic radiation, such as an ultraviolet (UV) orvisible light. The actinic radiation enters the photosensitive materialthrough the clear areas of the transparency and is blocked from enteringthe black or opaque areas. The exposed material crosslinks and becomesinsoluble to solvents used during image development. The unexposed,uncrosslinked photopolymer areas under the opaque regions of thetransparency remain soluble and are washed away with a suitablesolution, i.e., solvent or aqueous-based, leaving a relief imagesuitable for printing. Then the plate is dried. Alternatively, a “dry”thermal development process may be used to form the relief image inwhich the imagewise exposed photosensitive layer is contacted with anabsorbent material at a temperature sufficient to cause the compositionin the unexposed portions of the photosensitive layer to soften or meltand flow into the absorbent material. See U.S. Pat. Nos. 3,264,103(Cohen et al.); 5,015,556 (Martens); 5,175,072 (Martens); 5,215,859(Martens); and 5,279,697 (Peterson et al.). The exposed portions of thephotosensitive layer remain hard, that is, do not soften or melt, at thesoftening temperature for the unexposed portions. The absorbent materialcollects the softened un-irradiated material and then is separatedand/or removed from the photosensitive layer. The cycle of heating andcontacting the photosensitive layer may be repeated several times inorder to sufficiently remove the flowable composition from theun-irradiated areas and form a relief structure suitable for printing.The printing plate can be further treated to remove surface tackiness.After all desired processing steps, the plate is mounted on a cylinderand used for printing.

Flexographic printing forms made from photopolymerizable compositionswhich are soluble, swellable, or dispersible in aqueous, semi-aqueous,or organic solvent developers (so called wet development) may also becapable of liquifying upon thermal development to form the reliefsurface. Examples of suitable compositions for solvent development havebeen disclosed, for example, in Chen et al., U.S. Pat. No. 4,323,637,Grüetzmacher et al., U.S. Pat. No. 4,427,749 and Feinberg et al., U.S.Pat. No. 4,894,315.

In this embodiment where the imaging element forms a recording elementfor use as a flexographic printing form, the imaging element may includeone or more additional layers with the photosensitive layer. Thephotosensitive element may include one or more additional layers on theside of the photosensitive layer opposite a substrate support. Examplesof additional layers include, but are not limited to, a release layer, acapping layer, an elastomeric layer, a laser radiation-sensitive layer,an actinic radiation opaque layer, a barrier layer, and combinationsthereof. The one or more additional layers preferably are removable, inwhole or in part, during treatment to form the recording element. One ormore of the additional other layers can cover or only partially coverthe photosensitive composition layer. An example of an additional layerwhich only partially covers the photosensitive composition layer is amasking layer that is formed by imagewise application, e.g., ink jetapplication, of an actinic radiation blocking material or ink.

Additional Layers

The support can be any flexible material that is conventionally usedwith the imaging element used to prepare the recording element. Examplesof suitable support materials include polymeric films such those formedby addition polymers and linear condensation polymers, transparentfoams, fabrics, and metals. The support can be single layer ormultilayer, and can be in any form. A preferred support is a polyesterfilm; particularly preferred is polyethylene terephthalate.

For imaging elements used for flexographic printing, the support can beany flexible material that is conventionally used with photosensitiveelements used to prepare flexographic printing forms. Preferably thesupport is transparent to actinic radiation to accommodate “backflash”exposure through the support. Examples of suitable support materialsinclude polymeric films such those formed by addition polymers andlinear condensation polymers, transparent foams and fabrics. Undercertain end-use conditions, metals such as aluminum, may also be used asa support, even though a metal support is not transparent to radiation.A preferred support is a polyester film; particularly preferred ispolyethylene terephthalate. The support may be in sheet form or incylindrical form, such as a sleeve. The sleeve may be formed from singlelayer or multiple layers of flexible material. Flexible sleeves made ofpolymeric films are preferred, as they typically are transparent toultraviolet radiation and thereby accommodate backflash exposure forbuilding a floor in the cylindrical printing element. Sleeves suitablefor use as the support is not limited, provided that the sleeve meetsdesired functionality in end-use. The sleeve is not limited by thestructure or the materials of construction, and can include single andmultiple layered sleeves. An example of a multiple layered sleeve isdisclosed in U.S. Pat. No. 5,301,610. The sleeve may also be made ofnon-transparent, actinic radiation blocking materials, such as nickel orglass epoxy. The support typically has a thickness from 0.002 to 0.050inch (0.0051 to 0.127 cm). A preferred thickness for the sheet form is0.003 to 0.016 inch (0.0076 to 0.040 cm). The sleeve typically has awall thickness from 10 to 80 mils (0.025 to 0.203 cm) or more. Preferredwall thickness for the cylinder form is 10 to 40 mils (0.025 to 0.10cm).

Optionally, the imaging element includes an adhesive layer between thesupport and the photosensitive layer, or a surface of the support thatis adjacent the photosensitive layer has an adhesion-promoting surface.The adhesive layer on the surface of the support can be a subbing layerof an adhesive material or primer or an anchor layer as disclosed inU.S. Pat. No. 2,760,863 to give strong adherence between the support andthe photopolymerizable layer. The adhesive compositions that aredisclosed by Burg in U.S. Pat. No. 3,036,913 are also effective.Alternatively, the surface of the support on which thephotopolymerizable layer resides can be treated to promote adhesionbetween the support and the photopolymerizable layer, withflame-treatment or electron-treatment, e.g., corona-treated. Further,the adhesion of the photopolymerizable layer to the support can beadjusted by exposing the element to actinic radiation through thesupport as disclosed by Feinberg et al. in U.S. Pat. No. 5,292,617.

The imaging element may further include a temporary coversheet on top ofthe uppermost layer of the element, which uppermost layer may be thephotopolymerizable layer, or any of the additional layers. One purposeof the coversheet is to protect the uppermost layer of the imagingelement during storage and handling. The temporary coversheet may beremoved by peeling it away from the element prior to or after imagewiseexposure. For digital-to-plate image processing, the coversheet isremoved prior to exposing the infrared-sensitive layer to infrared laserradiation. Examples of suitable materials for the coversheet include athin film of polystyrene, polyethylene, polypropylene, polycarbonate,fluoropolymer, polyamide, or polyester, which film can be subbed withrelease layers. The coversheet is preferably prepared from polyester,such as Mylar® polyethylene terephthalate film; most preferably thecoversheet is 2-mil thick Mylar® film.

For imaging elements useful as flexographic recording (or printing)elements, the surface of the photopolymerizable layer may be tacky and arelease layer having a substantially non-tacky surface can be applied tothe surface of the photopolymerizable layer. Such release layer canprotect the surface of the photopolymerizable layer from being damagedduring removal of an optional temporary coversheet and can ensure thatthe photopolymerizable layer does not stick to the coversheet. Duringimage exposure, the release layer can prevent the image-bearing maskfrom binding with the photopolymerizable layer. The release layer isinsensitive to actinic radiation. The release layer is also suitable asa first embodiment of the barrier layer which is optionally interposedbetween the photopolymerizable layer and the actinic radiation opaquelayer. The elastomeric capping layer may also function as a secondembodiment of the barrier layer. Examples of suitable materials for therelease layer are well known in the art, and include polyamides,polyvinyl alcohol, hydroxyalkyl cellulose, copolymers of ethylene andvinyl acetate, amphoteric interpolymers, and combinations thereof.

The imaging element includes at least one photosensitive layer that canbe of a bi- or multi-layer construction. Further, the imaging elementmay include an elastomeric capping layer on the at least onephotopolymerizable layer. The elastomeric capping layer should have anelastic modulus in the polymerized state not substantially less than theelastic modulus of the photopolymerizable layer in the exposed state.The composition of the elastomeric layer comprises an elastomericpolymeric binder, an optional second polymeric binder and optionally anonmigratory dye or pigment. The elastomeric composition can alsocontain a monomer or monomers and a photoinitiating system. Theelastomeric polymeric binder in the elastomeric composition is generallythe same as or similar to the elastomeric binder present in thephotopolymerizable layer. The elastomeric capping layer is typicallypart of a multilayer cover element that becomes part of thephotosensitive printing element during preparation of thephotopolymerizable layer. Such multilayer cover elements andcompositions suitable as the elastomeric capping layer are disclosed inGruetzmacher et al., U.S. Pat. No. 4,427,759 and U.S. Pat. No.4,460,675. Although the elastomeric capping layer may not necessarilycontain photoreactive components, the layer ultimately becomesphotosensitive when in contact with the photopolymerizable layer. Assuch, upon imagewise exposure to actinic radiation, the elastomericcapping layer has portions in which polymerization or crosslinking haveoccurred and portions which remain unpolymerized, i.e., uncrosslinked.The elastomeric capping layer is similar to the photosensitive layer inthat after imagewise exposure the elastomeric capping layer is at leastpartially removable during treatment to form the relief.

In one embodiment of imaging elements useful as flexographic recordingelements, the laser radiation sensitive layer is sensitive to infraredlaser radiation, and may be identified as an infrared-sensitive layer,or as a mask forming layer. The laser radiation sensitive layer can beon the photosensitive layer, or on a barrier layer which is on thephotosensitive layer, or on a temporary support which together with thephotosensitive element form an assemblage. Infrared-sensitive layers andactinic radiation opaque layers are well known in the art. Theinfrared-sensitive layer can be ablated (i.e., vaporized or removed)from the photosensitive layer on the side opposite the flexiblesubstrate by exposure to infrared laser radiation. Alternatively, whenthe photosensitive element forms an assemblage with the support carryingthe infrared-sensitive layer, the infrared-sensitive layer can betransferred from the temporary support to the external surface (the sideopposite the flexible substrate) of the photosensitive layer by exposureto infrared laser radiation. The infrared-sensitive layer can be usedalone or with other layers, e.g., ejection layer, heating layer, etc.

The infrared-sensitive layer generally comprises an infrared-absorbingmaterial, a radiation-opaque material, and an optional binder. Darkinorganic pigments, such as carbon black and graphite, generallyfunction as both infrared-sensitive material and radiation-opaquematerial. The thickness of the infrared-sensitive layer should be in arange to optimize both sensitivity and opacity to actinic radiation(e.g., has an optical density of ≧2.5). Such infrared-sensitivephotoablative or phototransferable layer can be employed in digitaldirect-to-plate image technology in which the exposure by laserradiation removes or transfers the infrared-sensitive layer to form anin-situ mask on the photosensitive element. Suitable infrared-sensitivecompositions, elements, and their preparation are disclosed in U.S. Pat.No. 5,262,275;U.S. Pat. No. 5,719,009; U.S. Pat. No. 5,607,814; U.S.Pat. No. 5,506,086; U.S. Pat. No. 5,766,819; U.S. Pat. No. 5,840,463;and EP 0 741 330 A1. The infrared-sensitive layer preferably isremovable by contact with an absorbent material in the range ofacceptable developing temperatures for the photosensitive element used.

The one or more additional layers preferably are removable, in whole orin part, during treatment to form the relief image. That is the bycontact with the development medium in the range of acceptabledeveloping temperatures for the photosensitive element used.

Process of Use

The presence of the photoluminescent tag in the imaging element can beused to identify the element, which can then correspondingly be used todirect one or more conditions in a device or devices used to prepare arecording element from the imaging element.

An advantage of the present invention is that the optimum processconditions can be set for each element with minimal intervention by theuser. The conditions used in the process-of-use steps to convert theimaging element to the recording element can be set to maximizeperformance of the imaging element, based on information provided by thephotoluminescent tag. The method for making the recording elementincludes providing the imaging element of the present invention,exposing the imaging element to the actinic radiation, and treating theexposed element to form the recording element. The treating step is notlimited, and includes conventional steps to transform the exposedimaging element into the desired recording element. Treating can includetreatment with one or more solutions, such as washout, and etching;peeling; laminating; applying heat, etc. as appropriate for theparticular type of imaging element that converts the imagedphotosensitive layer to a readable recording element. The solutions fortreating the imaging element can be water, basic solutions, acidsolutions, aqueous-based solutions, semi-aqueous based, and solvent.

In the embodiment in which the imaging element forms a recording elementfor use as a flexographic printing form, the method for making aflexographic printing form comprising the steps of (a) imagewiseexposing the imaging element of the present invention to actinicradiation to selectively polymerize portions of the photopolymerizablelayer; and (b) treating the element resulting from step (a) to removeunpolymerized portions of the photopolymerizable layer to form a reliefimage. In one embodiment, the exposure step a) uses a source of actinicradiation that has at least one wavelength that is capable of elicitinga response of the photoluminescent tag.

In order to make the flexographic printing form, the imaging element ofthe present invention is exposed to actinic radiation from suitablesources. A mercury vapor arc or a sunlamp can be used at a distance ofabout 1.5 to about 60 inches (about 3.8 to about 153 cm) from thephotosensitive printing element. Exposure temperatures are preferablyambient or slightly higher, i.e., about 20° C. to about 35° C. Exposuretime can vary from a few seconds to tens of minutes, depending on theintensities and wavelengths of the actinic radiation, the nature andvolume of the photopolymerizable layer, the desired image resolution,and the distance from the photosensitive printing element. The exposureprocess usually comprises a back exposure and a front image-wiseexposure, although the former is not strictly necessary. The backexposure or “backflash” can take place before, after or duringimage-wise exposure. Backflash prior to image-wise exposure is generallypreferred. Back flash time can range from a few seconds to about 10minutes, and creates a shallow layer of polymerized material, or afloor, on the support side of the photopolymerizable layer andsensitizes the photopolymerizable layers and the support, helpshighlight dot resolution and also establishes the depth of the platerelief. The floor improves adhesion of the photopolymerizable layer tothe support, and provides better mechanical integrity to thephotosensitive element.

Imagewise exposure can be carried out by exposing the photosensitiveprinting element through an image-bearing mask, which may be referred toas an analog exposure or process. The image-bearing mask, a black andwhite transparency or negative containing the subject matter to beprinted, can be made from silver halides films or other means known inthe art. The image-bearing mask is placed on top of the photosensitiveprinting element after first stripping off the temporary coversheet.Imagewise exposure can be carried out in a vacuum frame, which providesproper contact of the image-bearing mask and the top surface of thephotosensitive printing element, and removes atmospheric oxygen which isknown to interfere with the free-radical polymerization process. Thephotosensitive printing element is then exposed to actinic radiation. Onexposure, the transparent areas of the negative allow additionpolymerization or crosslinking to take place, while the opaque areasremain uncrosslinked. Exposure is of sufficient duration to crosslinkthe exposed areas down to the support or to the back exposed layer.Imagewise exposure time is typically much longer than backflash time,and ranges from a few to tens of minutes.

Direct-to-plate image formation as disclosed in U.S. Pat. No. 5,262,275;U.S. Pat. No. 5,719,009; U.S. Pat. No. 5,607,814; van Zoeren, U.S. Pat.No. 5,506,086; and EP 0 741 330 A1, may also be referred to as digitalexposure or process. For the digital process, the presence of theinfrared-sensitive (and/or radiation opaque) layer is required. Animage-bearing mask is formed directly onto the infrared-sensitive layerin situ using an infrared laser exposure engine. Imagewise exposure ofprinting forms through such a photoablative mask can be done withoutusing a vacuum frame, simplifying the printing plate making process. Theexposure process involves (1) imagewise ablating the infrared-sensitivelayer of the photosensitive printing element described above to form amask; and (2) overall exposing the photosensitive element to actinicradiation through the mask. The exposure can be carried out usingvarious types of infrared lasers, which emit in the range 750 to 20,000nm, preferably in the range 780 to 2,000 nm. Diode lasers may be used,but Nd:YAG lasers emitting at 1060 nm are preferred.

Actinic radiation sources encompass the ultraviolet, visible andinfrared wavelength regions. The suitability of a particular actinicradiation source is governed by the photosensitivity of the initiatorand the at least one monomer used in preparing the imaging element. Thepreferred photosensitivity of most common flexographic printing forms isin the UV and deep visible area of the spectrum, as they afford betterroom-light stability. Examples of suitable visible and UV sourcesinclude carbon arcs, mercury-vapor arcs, fluorescent lamps, electronflash units, electron beam units, lasers, and photographic flood lamps.The most suitable sources of UV radiation are the mercury vapor lamps,particularly the sun lamps. Examples of industry standard radiationsources include the Sylvania 350 Blacklight fluorescent lamp(FR48T12/350 VL/VHO/180, 115w), and the Philips UV-A “TL”-serieslow-pressure mercury-vapor fluorescent lamps. These radiation sourcesgenerally emit long-wave UV radiation between 310-400 nm. Flexographicprinting plates sensitive to these particular UV sources use initiatorsthat absorb between 310-400 nm. It is contemplated that the imagewiseexposure to infrared radiation for those embodiments which include theinfrared-sensitive layer and the overall exposure to actinic radiationcan be carried out in the same equipment. It is preferred that this isdone using a drum, i.e., the photosensitive printing element is mountedon a drum which is rotated to allow for exposure of different areas ofthe photosensitive printing element.

Following overall exposure to UV radiation through the image-bearingmask, the photosensitive printing element is treated to removeunpolymerized areas in the photopolymerizable layer and thereby form arelief image. Treatment of the photosensitive printing element caninclude (1) “wet” development wherein the photopolymerizable layer iscontacted with a suitable developer solution to washout unpolymerizedareas and (2) “dry” development wherein the photopolymerizable layer isheated to a development temperature which causes the unpolymerized areasto melt or soften and is contacted with an absorbent material to wickaway the unpolymerized material. Dry development may also be calledthermal development. Wet development is usually carried out at aboutroom temperature. The developer solution can include an organic solvent,an aqueous or a semi-aqueous solution, or water. The choice of thedeveloper solution will depend primarily on the chemical nature of thephotopolymerizable composition to be removed. A suitable organic solventdeveloper includes an aromatic or an aliphatic hydrocarbon, an aliphaticor an aromatic halohydrocarbon solvent, or a mixture of such solventswith a suitable alcohol. Other organic solvent developers have beendisclosed in published German Application 38 28 551. A suitablesemi-aqueous developer can contain water and a water miscible organicsolvent and an alkaline material. A suitable aqueous developer cancontain water and an alkaline material. Other suitable aqueous developersolution combinations are described in U.S. Pat. No. 3,796,602.

Development time can vary, but it is preferably in the range of about 2to about 25 minutes. The developer solution can be applied in anyconvenient manner, including immersion, spraying, and brush or rollerapplication. Brushing aids can be used to remove the unpolymerizedportions of the photosensitive printing element. Washout can be carriedout in an automatic processing unit which uses developer and mechanicalbrushing action to remove the unexposed portions of the resultingflexographic printing plate, leaving a relief constituting the exposedimage and the floor.

Following treatment by developing in solution, the flexographic printingplates are generally blotted or wiped dry, and then more fully dried ina forced air or infrared oven. Drying times and temperatures may vary,however, typically the plate can be dried for about 60 minutes to about120 minutes at about 60° C. High temperatures are not recommendedbecause the support can shrink, and this can cause registrationproblems.

In thermal development, the photopolymerizable layer can be heated to adevelopment temperature typically between about 40° C. and 200° C. whichcauses the unpolymerized areas to liquefy, that is, to melt, soften, orflow. The photopolymerizable layer can then be contacted with adevelopment material to remove the unpolymerized photopolymerizablecomposition. The polymerized areas of the photopolymerizable layer havea higher melting temperature than the unpolymerized areas and thereforedo not melt at the development temperatures (see U.S. Pat. No. 5,215,859and WO 98/13730). Apparatus suitable for thermal development ofphotosensitive printing elements is disclosed in U.S. Pat. No. 5,279,697and U.S. Pat. No. 6,797,454.

In another alternate embodiment the imaging element may be suitablyreinforced and then imagewise exposed to laser radiation to engrave orremove the reinforced layer in depth imagewise. U.S. Pat. No. 5,798,202;U.S. Pat. No. 5,804,353; and U.S. Pat. No. 6,757,216 B2 disclosesuitable processes for making a flexographic printing plate by laserengraving a reinforced elastomeric layer on a flexible support. Theprocesses disclosed in U.S. Pat. Nos. 5,798,202 and 5,804,353 involvereinforcing and laser engraving a single-layer, or one or more layers ofa multi-layer, of a flexographic printing element comprised of areinforced elastomeric layer on a flexible support. The elastomericlayer is reinforced mechanically, or thermochemically, orphotochemically or combinations thereof. Mechanical reinforcement isprovided by incorporating reinforcing agents, such as finely dividedparticulate material, into the elastomeric layer. Photochemicalreinforcement is accomplished by incorporating photohardenable materialsinto the elastomeric layer and exposing the layer to actinic radiation.Photohardenable materials include photocrosslinkable andphotopolymerizable systems having a photoinitiator or photoinitiatorsystem.

The flexographic printing forms made using the imaging element of thepresent invention can be uniformly post-exposed to ensure that thephotopolymerization process is complete and that the photosensitiveprinting element will remain stable during printing and storage. Thispost-exposure step can utilize the same radiation source as the mainexposure.

Detackification is an optional post-development treatment which can beapplied if the surface of the flexographic printing plate is stilltacky, such tackiness not generally being removed in post-exposure.Tackiness can be eliminated by methods well known in the art, such astreatment with bromine or chlorine solutions, and by exposure toradiation sources having a wavelength not longer than 300 nm.

The imaging element of the present invention is particularly useful informing the recording element for flexographic printing on surfaceswhich are soft and easily deformable, such as packaging materials, e.g.,cardboard and plastic films. The photosensitive printing elements of thepresent invention can be used in the formation of seamless, continuousflexographic printing forms. The present imaging elements in the form ofa flat sheet can be wrapped around a cylindrical form, usually aprinting sleeve or the printing cylinder itself, and its edges fusedtogether to form a seamless, continuous photosensitive printing element.In a preferred method, the photopolymerizable layer is wrapped aroundthe cylindrical form and the edges joined. One process for joining theedges has been disclosed in German patent DE 28 44 426. Thephotopolymerizable layer can then be spray coated with at least oneadditional layer as described herein, if desired.

As was described above, in the embodiment where the imaging elementforms a recording element suitable for use as a flexographic printingform several possible structures of the imaging element are possible.The selection of the photoluminescent tag used in the element can beinfluenced by one or more of the process steps that the imaging elementwill undergo to form the printing form. The photoluminescent tag has anabsorption spectra that overlaps, in part or in whole, with anabsorption spectra of a source of radiation used to expose or otherwisecause a chemical or physical change in the imagine element (or recordingelement). The photoluminescent tag is responsive to at least onewavelength emitted from the source of radiation.

When imaging the photosensitive element a variety of electromagneticradiation wavelengths may be used. For example, in the case ofphotopolymer printing plates as an imaging element there can be multiplewavelengths used to produce a relief printing form based on the platemaking process and the type of mask (if needed). Table 1 lists the firstwavelengths of radiation, λ₁, that may be necessary to image theprinting plate as well as optional wavelengths, λ_(D), that aretypically needed based on the platemaking process used.

TABLE 1 Typical Wavelengths for Imaging Flexographic Printing ElementPlatemaking Process Type of Mask λ₁ λ_(D) Analog phototool or film UV(250-400 nm) Not applicable negative Digital Ablative mask UV (250-400nm) near-IR (800- 1100 nm) Engraved No Mask may need UV near-IR (800-(250-400 nm) 1100 nm) or IR (about 10600 nm) wherein: λ₁ Firstwavelength used in the imaging of the photosensitive element λ_(D)Optional additional wavelength used in the imaging of the photosensitiveelement

Consequently, based on the imaging process, the source of the at leastone wavelength that causes the response of the tag needs to be chosen.The photoluminescent tag is responsive to at least one wavelength ofradiation, that is, the tag is stimulated or excited at the responsivewavelength, λ_(R). For example, the choice of responsive wavelength canbe limited by the wavelength of radiation, λ₁, used for the primaryphotosensitive system, and may optionally be also limited by the one ormore additional wavelengths λ_(D), necessary to perform the process toconvert the imaging element to a recording element, as described inTable 2. For instance, when making a relief printing form from aphotopolymer printing precursor using a film negative in the analogplatemaking process, the first wavelength, λ₁, is in the UV region. Thephotoluminescent tag could be selected so that, the tag is responsive toat least one wavelength, λ_(R), in UV region emitted by the source of UVradiation. Provided that the response of the tag to the exposure to theUV radiation is to emit radiation at a wavelength that is not at thefirst wavelength λ₁, for example the tag emits radiation in the visible,or IR or near IR region, the response of the tag would not influence theimaging of the photosensitive material.

TABLE 2 Possible Choices of Response Wavelength of the PhotoluminescentTag in a Flexographic Printing Element Platemaking Process λ_(R) inrange λ_(e) in range Factors Impacting Choice of λ_(R) Analog UV(250-400 nm) Visible, IR, near IR level of tag in composition; size oftag (400-10600 nm) particulate; uniformity of disposition of tag in theimaging element; absorption characteristics of tag; emission orstimulation characteristics of tag Digital UV (250-400 nm) Visible, IR,near IR level of tag in composition; size of tag (400-10600 nm)particulate; uniformity of disposition of tag in the imaging element;absorption characteristics of tag; emission or stimulationcharacteristics of tag; absorption characteristics of (IR sensitivedigital layer) imaging element at λ_(e) Digital near-IR (800- Visible,IR, UV level of tag in composition; size of tag 1100 nm) particulate;uniformity of disposition of tag in the imaging element; absorptioncharacteristics of tag; emission or stimulation characteristics of tag;absorption characteristics of (photopolymerizable layer) imaging elementat λ_(e) Engraved UV (250-400 nm) Visible, IR, near IR level of tag incomposition; size of tag (400-10600 nm) particulate; uniformity ofdisposition of tag in the imaging element; absorption characteristics oftag; emission or stimulation characteristics of tag Engraved near-IR(800- Visible or UV level of tag in composition; size of tag 1100 nm) orparticulate; uniformity of disposition of IR (about 10600 tag in theimaging element; absorption nm) characteristics of tag; absorptioncharacteristics of imaging element at λ_(e) Legend: λ_(R) Responsivewavelength used to excite (or stimulate) the tag λ_(e) Emission orstimulation wavelength of the tag

Furthermore as shown Table 2, the photoluminescent tag must be carefullyselected for excitation by the responsive wavelength when the imagingelement will be exposed to wavelengths other than λ₁ in the process ofuse such as in the digital platemaking process or engraving process. Inone embodiment, the photoluminescent tag is chosen to be responsive toat least one wavelength that is needed for the imaging process. If thetag is responsive in the region of the spectrum that does overlap withthe first wavelength or the optional imaging wavelength (such as thelaser wavelength for digital imaging), provided that the tag is excitedor stimulated to emit radiation at a wavelength different than the firstwavelength or the optional wavelength, there is no potential forundesirable imaging of the element when the excitation process is beingperformed.

In one embodiment, the photoluminescent tag can be chosen to emitradiation in a region of the spectrum that is used to for other imagingsteps in preparing the recording element (such as the laser wavelengthfor digital imaging) provided that the concentration of the tag is suchthat the impact on the process operating at the optional wavelengthλ_(D) is made inconsequential. For example, by having the concentrationlevel in a range from 1-1000 ppm of the photoluminescent tag responsiveto IR radiation, the impact of the tag on the digital imaging process ismade inconsequential.

It is also contemplated that the photoluminescent tag can be chosen toemit radiation in a region of the spectrum that is used for actinicradiation in a previous step of the imaging process to convert theimaging element to a recording element. The tag can emit radiation in aregion of the spectrum that is used to expose the photosensitive element(such as the laser wavelength for digital imaging), upon exposure to UVradiation to photopolymerize the photosensitive layer.

The detection process is completed when the tag emits at a wavelength,λ_(e), that is read by the detection system.

DETECTION PROCESS

Any device that is used in the process of forming a recording image fromthe imaging element can include a detection system that scans theelement to sense the presence of the photoluminescent tag. It isgenerally preferred to use the same source of radiation that causes thephotoreactive response of the imaging element to also elicit theresponse of the tag to have excited or stimulated emission. Typicallythis would entail that the source of radiation that provides the actinicradiation for the composition and the response of the tag originates inan exposure device. However, it is also contemplated that a separatesource of radiation equivalent or substantially equivalent to the sourceof actinic radiation can be used to elicit the response of the tag in adevice other than an exposure device. In one embodiment, the separatesource of radiation could be used providing that at least thecomposition of the imaging element had already been exposed to theactinic radiation. In another embodiment, the separate source ofradiation could be used in a device other than an exposure unit, if theimaging element includes a portion that is not used for the recordingelement, that is, the element includes a portion that is used only toexpose the composition and elicit a response of the tag, such as adetecting strip.

The detection system, which can include a scanner and/or sensor, is notlimited provided that the system can irradiate the imaging element withradiation suitable to excite the photoluminescent tag, and preferablyalso can detect the radiation emitted by the tag. Alternatively, thefunctions of scanning and sensing may be separated into differentcomponents within a process device. One component may be used toirradiate the imaging element and another component may be used to sensethe emitted radiation. One type of suitable detection system arefluorospectrophotometers. It is important that the capability of thedetection system, that is the exposing radiation wavelength (range) andthe detecting radiation wavelength (range), correspond to the capabilityof the photoluminescent tag, that is, the exciting wavelength andemitting wavelength, respectively. Optionally, the detection system canbe independent of the device used to produce the recording element, butelectronically transmit information about the imaging element to thedevice. The device would include a programmable logic controllerconnected to a control console and the scanner/sensor. The controllermay include a modem for connection to an external data communicationsnetwork. The modem makes it possible to remotely collect operating datafrom, and provide commands to, the controller. The device may include awireless communication device, such as for example, a radio-frequencycommunication device or other form, that could transmit data to thelocal area network which may be connected to other secondary processingdevices that are needed to create the recording element. Thescanner/sensor is set to scan the imaging element, receives thecharacteristic tag response, which identifies the imaging element andone or more characteristics of the element. In the case of imagingelements that are printing plates, the characteristic tag response canidentify the chemical formulation (type) of the element, the totalthickness of the element, a width of the element, and desired reliefdepth for the finished recording element.

The detection system not only can be used to identify the imagingelement, but also can provide information that in combination with acontroller or software containing data sets, is used to direct theestablishment of the parameters in the variety of devices used in theimaging process automatically without the need for human intervention.The characteristic tag information can be used to determine or recommendthe appropriate conditions needed at one or more steps in the process totransform the imaging element into the recording element. Thecharacteristic tag response information can be used to recommend orestablish appropriate conditions in one or more exposure units, laserexposure devices, development processors, and laminators, that are usedwith the imaging element. For instance, the characteristic tag responsecan be used to recommend or determine the appropriate conditions neededto expose the imaging element such as exposure time and energy level.The characteristic tag response of the imaging element for use as aflexographic printing form can also be used to recommend or determineappropriate conditions needed for thermal processing, such as thedevelopment temperature, pressure, drum rotation speed, and number ofcycles of heating and contacting; or the conditions appropriate forsolvent processing such as brush pressure, brush height, and residencetime of element in solvent. The characteristic tag response can also beused to establish set-up parameters or recommend conditions appropriatefor laser imagers or engraving devices such as laser settings and drumrotation speed. The characteristic tag response can also be used toestablish set-up parameters or recommend conditions appropriate forlaminators such as pressure, temperature, and transport speed. Each stepof the transforming the imaging element into a recording element,involves multiple variables which need to be set properly to extractoptimum performance of the imaging element and create the desiredrecording element. It is desirable to provide an imaging element andsystem that can, with little invention by the user, set the neededprocess conditions. In this way the imaging element can be transformedinto recording element with improved control of the process andconsistent quality in the resulting recording elements.

There are other useful applications of this information as well. Thescanner/sensor system may also transmit by a direct connection, or viamodem, or via wireless communication, to a computer or data storagemodule the type and quantity of imaging elements used in the variousdevices in the process. This accumulation of data can be very useful intracking and monitoring the stage of the process that a given imagingelement may be undergoing. Also, by assimilating the type and quantityof imaging elements processed a user could track inventory levelsautomatically. In combination with wired or wireless communicationnetworks this automatic inventory tracking capability could be combinedwith automated ordering and inventory replenishment processes that arehighly valuable in many operations. The information regarding theimaging element (type, thickness, etc) can be combined with otherknowledge that is either readily available or can be obtained regardingthe intended image to further optimize the workflow and/or theprocessing conditions used in the process of producing the recordingelement.

EXAMPLES Example 1

The following mixture was prepared: 75% of apoly(styrene/isoprene/styrene) binder, 11.825% of polyisoprene oil(Mw=30,000), 9% of a diacrylic monomer, 2.5% of a photoinitiator(Irgacure® 651, a benzyldimethylketal from Ciba), 0.025% of aphotoluminescent tag (SpectraGreen from Spectra Systems), 1.5% of athermal stabilizer, and 0.15% of a solution of inert dye. The inert dyeprovided a pink-red color to the mixture. The photoinitiator was usedfor crosslinking the mixture during the main exposure step and had anabsorption maximum at 365 nm (range of 340-380 nm), and thephotoluminescent tag had an absorption maximum at 370 nm (range of about360-380 nm).

The mixture was extruded and calendered to form a photosensitive elementhaving a photopolymerizable layer between a support of Mylar® (5 mils)and a coversheet (7 mils). The coversheet included a release layer ofMacromelt® polyamide that was adjacent the photopolymerizable layer. Thetotal thickness of the element was 72 mils. The element obtained wasbackflash exposed to UV light for 30 seconds (0.6 joules/cm²) on aCYREL® exposure unit to form a floor. The exposure unit included asource of UV light from a fluorescent lamp that emitted radiationbetween 320 to 380 nm, for the main and backflash exposures. Thecoversheet was removed, and an image-bearing negative was placed on asurface of the element opposite the support, and a vacuum was drawn. Theelement was main exposed to the UV light source through the negative for10 minutes (7.2 joules/cm²) on the exposure unit. Upon both thebackflash exposure and the main exposure, the element emitted a greenvisible light, indicating that the photoluminescent tag was stimulatedby the UV light source to emit in 530-560 nm.

The element was developed in organic solvent, CYREL® OPTISOL washoutsolution for 420 seconds in a CYREL 1002 type processor to remove theunexposed areas and form a relief printing plate. The plate was thendried for 2 hours in a convection oven. After drying, the plate wasfurther exposed to UV radiation (254 nm) 240-260 nm range on theexposure unit for 4 minutes to light finish eliminating any residualtackiness. The photoluminescent tag did not emit when the plate wasexposed to the source of radiation having 254 nm wavelength.

The presence of the photoluminescent tag in the photosensitive elementhad no discernable effect on the process to form a flexographic printingplate since a relief surface having desired image quality was formed.

Example 2

The following mixture was prepared: 70% of apoly(styrene/butadiene/styrene) binder, 16% of polybutadiene oil(Mw=1,000), 9.825% of a diacrylic monomer, 2.5% of a photoinitiator(Irgacure® 651, a benzyldimethylketal from Ciba), 0.025% of aphotoluminescent tag (SpectraBlue from Spectra Systems), 1.5% of athermal stabilizer, and 0.15% of a solution of inert dye. The inert dyeprovided a pink-red color to the mixture. The photoinitiator was usedfor crosslinking the mixture during the main exposure step and had anabsorption maximum at 365 nm (range of 340-380 nm), and thephotoluminescent tag had an absorption maximum at 370 nm (range of about360-380 nm).

The mixture was extruded and calendered to form a photosensitive elementhaving a photopolymerizable layer between a support of Mylar® (5 mils)and a coversheet (7 mils). The coversheet included a release layer ofMacromelt® polyamide, which was adjacent the photopolymerizable layer.The total thickness of the element was 72 mils. The element obtained wasbackflash exposed to UV light for 30 seconds (0.6 joules/cm²) on aCYREL® exposure unit to form a floor. The exposure unit included asource of UV light from a fluorescent lamp, which emitted radiationbetween 320 to 380 nm. The coversheet was removed, and an image-bearingnegative was placed on a surface of the element opposite the support,and a vacuum was drawn. The element was main exposed to the UV radiationsource through the negative for 10 minutes (7.2 joules/cm²) on theexposure unit. Upon both the backflash exposure and the main exposure,the element emitted a blue visible light, indicating that thephotoluminescent tag was stimulated by the UV light source to emit in460-480 nm.

The element was developed in organic solvent, CYREL® OPTISOL washoutsolution for 420 seconds in a CYREL 1002 type processor to remove theunexposed areas and form a relief printing plate. The plate was thendried for 2 hours in a convection oven. After drying, the plate wasfurther exposed to UV light (254 nm) on the exposure unit for 4 minutesto light finish eliminating any residual tackiness. The blue tag did notemit when the plate was exposed to this finishing wavelength.

The presence of the photoluminescent tag in the photosensitive elementhad no discernable effect on the process to form a flexographic printingplate since a relief surface having desired image quality was formed.

Example 3

The following mixture is prepared: 70% of apoly(styrene/butadiene/styrene) binder, 16% of polybutadiene oil(Mw=1,000), 9.825% of a diacrylic monomer, 2.5% of a photoinitiator(Irgacure® 651, a benzyldimethylketal from Ciba), 0.025% of aphotoluminescent tag of a europium chelate, Eu (III)[tri(2-naphthoyltrifluoroacetone) di(trioctylphosphineoxide)], 1.5% of athermal stabilizer, and 0.15% of a solution of inert dye. The inert dyeprovides a pink-red color to the mixture. The photoinitiator crosslinksthe mixture during the main exposure step and has an absorption maximumat 365 nm (range of 340-380 nm). The photoluminescent tag has anabsorption maximum at 370 nm (range of about 360-380 nm).

The mixture is extruded and calendered to form a photosensitive elementhaving a photopolymerizable layer between a support of Mylar® (5 mils)and a coversheet (7 mils). The coversheet includes a release layer ofMacromelt® polyamide, which will be adjacent the photopolymerizablelayer. The element is backflash exposed to UV light for 30 seconds (0.6joules/cm²) on a CYREL® exposure unit in order to form a floor. Theexposure unit includes a source of UV radiation from a fluorescent lampthat emits radiation between 320 to 380 nm. The coversheet is removed,and an image-bearing negative is placed on a surface of the elementopposite the support, under vacuum. The element is exposed to the UVlight source through the negative for 10 minutes (7.2 joules/cm²) on theexposure unit. After both the backflash and main exposures the elementemits a blue visible light, indicating that the photoluminescent tag isstimulated by the UV light source to emit in 460-480 nm.

The element is developed in organic solvent, CYREL® OPTISOL washoutsolution for 420 seconds in a CYREL 1002 type processor to remove theunexposed areas and form a relief printing plate. The plate is thendried for 2 hours in a convection oven. After drying, the plate isexposed to UV light (254 nm) on the exposure unit for 4 minutes to lightfinish to eliminate any residual tackiness. The blue tag does not emitwhen the plate is exposed to the finishing wavelength.

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 28. A method for settingconditions in a device used for making a recording element comprising:a) providing a precursor printing form comprising a layer of aphotopolymerizable composition sensitive to actinic radiation from asource of radiation having a range of wavelengths greater than 10 nm,wherein the photopolymerizable layer has a thickness range of 0.010 to0.250 inch, and wherein a photoluminescent tag excluding opticalbrighteners is disposed in the precursor printing form and is responsiveto at least one wavelength from the source of radiation, the compositionbeing sensitive to the at least one wavelength; b) exposing theprecursor printing form to the at least one wavelength to generate anemitted radiation from the tag at a wavelength that is different fromthe actinic radiation; c) detecting the emitted radiation; and d)setting one or more conditions for operation of the device according tothe detected emission from step c).
 29. The method of claim 28 whereinthe device having the source of actinic radiation is selected from thegroup consisting of an actinic radiation exposure unit; and a laserradiation exposure unit.
 30. The method of claim 28 wherein the settingstep comprises: d1) translating the detected emission of step c) into acoded signal; d2) interpreting the coded signal; and d3) responding tothe interpreted signal by establishing one or more of operatingconditions for the device.
 31. The method of claim 30 wherein theresponding step further comprises comparing one or more of theconditions against a corresponding baseline set point and/or range; anddetermining if one or more of the conditions is changed.
 32. The methodof claim 30 wherein the responding step further comprises changing oneor more of the operating conditions of the device.
 33. The method ofclaim 28 further comprising d4) responding to the interpreted signal byestablishing one or more of operating conditions for a second deviceused for making the recording element.
 34. The method of claim 33wherein the second device is selected from the group consisting of: athermal processor for heating the precursor printing form to atemperature sufficient to cause at least one area of the precursorprinting form to melt, flow or soften; a washout processor for removingat least one area of the precursor printing form with a solution; and alaminator for forming an assemblage of a secondary element with theprecursor printing form.
 35. The method of claim 28 wherein the deviceis selected from the group consisting of: a thermal processor forheating the precursor printing form to a temperature sufficient to causeat least one area of the precursor printing form to melt, flow orsoften; a washout processor for removing at least one area of theprecursor printing form with a solution; a laser radiation exposure unitfor forming an image on the precursor printing form; exposure unit forexposing the precursor printing form to the actinic radiation; and alaminator for forming an assemblage of a secondary element with theprecursor printing form.